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(Received for publication, July 26, 1995; and in revised form, August 23,
1995) From the
Rifampicin and streptolydigin are antibiotics which inhibit
prokaryotic RNA polymerase at the initiation and elongation steps,
respectively. In Escherichia coli, resistance to each
antibiotic results from alterations in the
The RNA polymerase core enzyme of eubacteria has a multisubunit
structure containing one One way to explore these structure-function relationships in
eubacteria is to study the action of two antibiotics that specifically
target RNA polymerase, rifampicin (Rif) In the Gram-negative bacterium Escherichia coli, mutations that confer either Rif resistance
(Rif Here we use in vitro mutagenesis to
establish that additional sites for Stl
Inspection of the DNA sequence revealed that
the
Figure 1:
Genetic organization of the B.
subtilis rpoB-rpoC region. The chromosome in the rpoB-rpoC region is represented by the heavy line and kilobase
scale. The rectangles above the physical map indicate the open
reading frames encoding ribosomal protein L7/12 (rplL), the
23,000-dalton protein P23 (orf23), the
To construct additional alterations, we replaced Primer 2A
with Primer 2G (5`-GTAGTGAACGTCACGCACTTCCATTCGGGCACG), Primer 2M
(5`-GTAGTGAACGTCACGCACTTCCCTTCCGGCACG), Primer 2E
(5`-GTAGTGAACGTCACGCACTACCATTCCGGCACG), or Primer 2
Coding regions were
identified by aligning the predicted B. subtilis products with
their E. coli counterparts(25) . As shown in Fig. 1, B. subtilis had a gene order similar but not
identical to E. coli, with the rpoC homologue
(encoding The proposed rpoC reading frame encodes a predicted
1,199-residue product that is 53% identical to E. coli
To locate the stl445 alteration more precisely, we made three additional
plasmids carrying portions of this 1-kb region. As shown in Fig. 1, these fragments were carried by plasmids pXY16, pXY19,
and pXY21. After transformation into wild-type strain PB2, linearized
plasmids pXY19 and pXY21 both yielded Stl Fig. 2shows a
comparison of Region F in B. subtilis
Figure 2:
Comparison of Region F among the largest
subunits of eukaryotic and prokaryotic RNA polymerases. The alignment
of the four eukaryotic sequences and the E. coli
The
results we report here and those in the accompanying paper (14) are consistent with this possibility. In addition to the
Stl
Figure 3:
Rif-Stl region of the B. subtilis and E. coli
Plasmids bearing five different alterations in this
region were constructed as described under ``Experimental
Procedures'' and introduced into the rpoB region of the B. subtilis chromosome by transformation. Only plasmids
bearing the A499V, G500R, or E502V alterations yielded Stl We characterized the three verified
mutants on tryptose blood agar base plates and found that they
manifested different levels of Stl This difference in resistance may reflect subtle differences in the
putative Stl binding sites in the two organisms. In this regard, our
inability to obtain Stl In B. subtilis
The nucleotide
sequence(s) reported in this paper has been submitted to the
GenBank(TM)/EMBL Data Bank with accession number(s)
L43593[GenBank].
Volume 270,
Number 41,
Issue of October 13, 1995 pp. 23930-23933
©1995 by The American Society for Biochemistry and Molecular Biology, Inc.
or
` Subunits of Bacillus subtilis RNA Polymerase (*)
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS AND DISCUSSION
FOOTNOTES
ACKNOWLEDGEMENTS
REFERENCES
subunit of the core
enzyme. However, in Bacillus subtilis, reconstitution studies
found rifampicin resistance (Rif
) associated with the
subunit and streptolydigin resistance (Stl) with `. To
understand the basis of bacterial Stl, we isolated the B. subtilis rpoC gene, which encodes a 1,199-residue product
that is 53% identical to E. coli `. Two spontaneous
Stl mutants carried the same D796G substitution in rpoC, and this substitution alone was sufficient to confer
Stlin vivo. D796 falls within Region F, which is
conserved among the largest subunits of prokaryotic and eukaryotic RNA
polymerases. Among eukaryotes, alterations in Region F promote
resistance to 
-amanitin, a toxin which inhibits transcription
elongation; among prokaryotes, alterations in Region F cause aberrant
termination. To determine whether alterations in the subunit of B. subtilis could also confer Stl, we made three
Stl substitutions (A499V, G500R, and E502V) in the rif region of rpoB. Together these results suggest that
and ` interact to form an Stl binding site, and that this site is
important for transcription elongation.
, one `, and two subunits (see (1) for a review). Most of the catalytic functions of the
enzyme are thought to reside in the two largest subunits, and
`. Because the and ` subunits share colinear blocks of
conserved sequence with the two largest subunits of eukaryotic RNA
polymerases, genetic and biochemical analysis of the eubacterial enzyme
can contribute to an understanding of the structure-function
relationships among RNA polymerases of all organisms(1) . 
and streptolydigin
(Stl), each of which has a different mechanism of inhibition. Rif
arrests transcriptional initiation at the promoter by locking RNA
polymerase in an abortive initiation complex capable of synthesizing
only short oligonucleotides, but this antibiotic has no effect once the
transcription complex has elongated past the promoter (2) . In
contrast, Stl blocks both transcriptional initiation and elongation by
inhibiting the translocation step, thereby reducing the rate of chain
formation. This translocation inhibition has been suggested to result
from interference with either the nucleotide triphosphate binding site
or the ability to form the phosphodiester bond between the incoming
triphosphate and the nascent RNA chain (3, 4, 5) .) or Stl resistance (Stl) have been mapped
to rpoB, the gene encoding the
subunit(6, 7, 8, 9, 10) .
Likewise, reconstitution studies in the Gram-positive bacterium Bacillus subtilis found that Rif is also
associated with the subunit, but that Stl is
associated with `(11, 12) . Because the primary
sequences of and ` are highly conserved between E. coli and B. subtilis(13) , it was reasonable to
presume that additional sites for Stl might lay within the
` subunit of E. coli and within the subunit of B. subtilis. in B. subtilis do map within rpoB, the gene encoding the subunit
of RNA polymerase. We also use molecular techniques to precisely map
two previously isolated Stl mutations within rpoC,
the gene encoding the ` subunit. Both Stl mutations in rpoC alter the same residue in a region highly conserved among
the largest subunits of prokaryotic and eukaryotic RNA polymerases. In
the accompanying paper, Severinov et al.(14) show
that newly isolated alterations to Stl also affect the same
conserved region in E. coli rpoC. Together with previous
results, these data suggest that the and ` subunits of
eubacterial RNA polymerase interact to form an Stl binding site.
Strains, Phage, and Genetic Methods
E. coli DH5 was host for plasmid constructions, and E. coli Y1090 was host for gt11 phage, grown as described
previously(15) . Streptolydigin, a gift of Laura Heisler and
Carol Gross, was incorporated into tryptose blood agar base plates
(Difco) at 3-50 µg/ml. Standard genetic and recombinant DNA
methods were performed as described previously(13) . Polymerase
chain reactions (PCR) were done using Taq polymerase (Promega,
Madison, WI) according to published protocols(16) , and the
resulting products were cloned into the pCR(TM) II vector
(Invitrogen, San Diego, CA). DNA sequencing was done on subcloned
fragments by one of two methods: (i) automated DNA sequencing using the
Applied Biosystems 373A with analysis software version 1.2, or (ii)
dideoxynucleotide chain termination with reactions primed on
double-stranded DNA templates, using the Sequenase enzyme and protocols
from U. S. Biochemical Corp. For direct genomic sequencing the
fmol(TM) DNA Sequencing System (Promega) was used as specified by
the manufacturer.
Isolation of the B. subtilis rpoC Gene
We
previously isolated a gt11 phage that carried the 5` third of rpoC(13) . To obtain the remaining portion of rpoC, we first amplified a 2.2-kb PCR product from the B.
subtilis genome using Primer A (5`-GAAGTTTGGGATGTACTAG) from the
available rpoC sequence together with degenerate Primer B
(5`-AGCAAGAGAAGCTTTNGTRATNCC), designed by comparing the conserved 3`
ends of the rpoC genes from E. coli(17) and Staphylococcus aureus(18) . This PCR probe was used to
screen a random library of B. subtilis chromosomal DNA carried
in
gt11(15) . One positive phage designated
gt11-21
was obtained; this phage carried a 2.8-kb insert from the B.
subtilis genome.
gt11-21 insert significantly extended the available rpoC sequence and lacked only the extreme 3` end of the gene. When
additional screening of the
libraries failed to identify an
overlapping clone bearing the missing region, we used PCR to directly
isolate and sequence the 3` end of rpoC and the 5` end of rpsL, which encodes ribosomal protein S12(19) . To
this end, degenerate Primer C (5`-GCAGACGCCACGWTTYTGNGG) was designed
by comparing the conserved portions of the S12 sequences from E.
coli(20) and Bacillus
stearothermophilus(21) . A 3.1-kb fragment was then
amplified from the B. subtilis chromosome using Primers A and
C. This fragment allowed extension of the rpoC sequence beyond
clone
gt11-21 by directly sequencing both strands from the
chromosome using the fmol(TM) DNA sequencing system.
Location of the Stl445 Allele within rpoC
B.
subtilis strain MO34 (stl445) and MO38 (stl6)
were provided by A. L. Sonenshein(22, 23) . Three
overlapping fragments covering the entire rpoC region were
amplified from the chromosome of MO34 by PCR. As shown in Fig. 1, these three fragments were subcloned into pCR(TM) II
to yield pXY11 (carrying the rpoC fragment extending from nt
4413 to 6216), pXY12 (nt 5924-8119), and PXY13 (nt
7347-8672). The resulting plasmids were linearized by digestion
with NcoI and transformed into the wild-type strain PB2 with
selection for Stl at 10 µg/ml. Only the fragment
carried by pXY12 conferred Stl at a significant frequency.
To locate the stl445 alteration within the pXY12 insert, the BamHI and HindIII sites (Fig. 1) were used to
construct pXY16 (from nt 5924 to the HindIII site at nt 6422),
pXY19 (from the HindIII site at nt 6422 to the BamHI
site at nt 7386), and pXY21 (from nt 6811 to the BamHI site at
nt 7386).
(rpoB)
and ` (rpoC) subunits of RNA polymerase, the 9,180-dalton
protein P9 (orf82), and ribosomal protein S12 (rpsL),
all of which are transcribed from left to right. The arrows adjacent to the L7/12 and S12 reading frames indicate that they
extend beyond the cloned region. The positions of the Rif-Stl region of
and conserved Region F of ` are denoted by the cross-hatched and shaded rectangles, respectively.
The triangle following Region F indicates the location of the
189-residue deletion of B. subtilis ` compared to the
sequence of the E. coli subunit. The horizontal lines beneath the restriction map show the regions of the chromosome of
strain MO34 (stl445) used in the plasmid constructions
described under ``Experimental Procedures''; the three
plasmids conferring Stl are labeled (+). The physical
map of the rpoB-rpoC region between 0 and 6.1 kb is from Boor et al.(13) , whereas the map from 6.1 to 9.0 kb was
derived from the DNA sequence of the chromosomal insert of the
gt11-21 phage and the PCR product shown by the light
horizontal lines at the bottom of the
figure.
Construction of Stl
We used a four-primer system of site-directed
mutagenesis (24) to construct alterations in B. subtilis Mutations in
rpoB residues 499-502(13) . For the A499V
alteration, we used pairs of primers to amplify two overlapping
fragments from the chromosome. Primer 1 (5`-TCGGCAATGCTTACATCGAAG,
corresponding to the coding region for residues 364-370)
was first used with Primer 2A
(5`-GTAGTGAACGTCACGCACTTCCATTCCGACACG, complementary to the
coding region for residues 498-508). Primer 2A bears a transition
from G to A (underlined) that leads to substitution of valine for
alanine at residue 499. Then Primer 3 (5`-GTGCGTGACGTTCAC,
corresponding to residues 503-508) was used with Primer 4
(5`-TTTGGCTTCTACGCGTTC, complementary to residues 683-688). The
resulting two fragments were mixed and further amplified using Primer 1
and Primer 4, yielding the A499V alteration on a 957-base pair
fragment.
(5`-GTAGTGAACGTCACGCAC[]ACGCTCACGTGTCAATCC), each
containing either a single mutation (underlined) or a deletion of the
12 base pairs coding for residues 499-502 (). Each of these
PCR-mutagenized products was cloned into the pCR(TM) II vector,
resulting in plasmids pXY31 (containing the A499V alteration), pXY32
(G500R), pXY33 (M501S), pXY34 (E502V), and pXY35 (499-502).
These plasmids were linearized with NcoI and transformed into
the B. subtilis wild type strain PB2 with selection for
Stl (5 µg/ml).
A Different Organization of the B. subtilis rpoC
Region
We previously described the isolation of the B.
subtilis rpoB gene and the 5` third of rpoC(13) .
To address the question of whether Stl could be conferred
by alterations in either the or ` subunits of RNA
polymerase, we first used chromosomal walking methods to isolate the
remainder of rpoC and the downstream rpsL gene. As
shown in Fig. 1, the resulting fragments carried overlapping
regions of the B. subtilis chromosome, which bore the 3`
two-thirds of the ` coding region.`) followed by an open reading frame (orf82)
that could encode a protein of 82 residues (P9). This P9 reading frame
was in turn closely followed by the rpsL homologue (encoding
ribosomal protein S12). The predicted sequence of P9 was significantly
similar (28% identity in a 71-residue overlap; z value of 10.6
standard deviations above the mean of a shuffled sequence) to a
hypothetical ribosomal protein encoded by orf104, which
occupies a similar position downstream of the rpoC homologue
in Sulfolobus acidocaldarius(26) . However, the P9
reading frame is entirely absent from the equivalent E. coli region, where rpoC is directly followed by rpsL. ` (17) and 55% identical to Mycobacterium leprae `(27) . Moreover, all three ` sequences share
the eight regions (A through H) that are highly conserved among the
largest subunits of eubacterial and eukaryotic RNA polymerases
(nomenclature according to (28) ). Notably, as shown in Fig. 1, the ` subunit from the Gram-positive B.
subtilis lacks a 189-residue segment found between conserved
regions G and H in the equivalent subunit of the Gram-negative E.
coli. The ` subunit from the Gram-positive M. leprae also lacks this segment(27) . The complete absence of this
segment from the Gram-positive lineage suggests that it is not
essential for minimal ` function.Stl
Two spontaneous StlMutations Map within a Highly
Conserved Region of rpoC That Is Important for Transcriptional
Elongation mutations, stl445 and stl6, were previously isolated by A. L.
Sonenshein and colleagues(22, 23) , and they kindly
supplied strains bearing these alleles. To first establish whether
alterations in the ` subunit could indeed confer Stl on B. subtilis RNA polymerase in vivo as
suggested by subunit reconstitution experiments (12) , we made
three overlapping PCR fragments that carried the entire rpoC coding sequence. For these experiments, chromosomal DNA from the
Stl strain MO34 (stl445) was used as a template.
As shown in Fig. 1, these overlapping fragments were carried by
plasmids pXY11, pXY12, and pXY13. To identify the fragment containing
the stl445 alteration, these plasmids were linearized so that
they could replace the homologous rpoC region on the B.
subtilis chromosome via a double crossover event. Upon
transformation into the wild-type strain PB2, only plasmid pXY12
conferred Stl at a frequency significantly higher (50-fold)
than the control plasmids, which bore the same three fragments isolated
from the wild-type, Stl
strain (not shown). We inferred
from these results that the stl445 alteration lay within the
1-kb rpoC fragment that was unique to pXY12 and was not
present on the other two plasmids (see Fig. 1). transformants at
a frequency significantly higher than the control plasmids. We
concluded that the stl445 alteration lay within the 565-nt rpoC fragment common to both pXY19 and pXY21. Analysis of this
fragment revealed only a single transition from the wild-type sequence,
an A to a G at nt 7118. This transition would lead to substitution of a
glycine for an aspartate at residue 796 of B. subtilis `
(D796G). We directly sequenced the corresponding region of the MO34 (stl445) parent chromosome and confirmed that it was identical
to wild type except for the A to G transition at nt 7118. Furthermore,
this sequenced region again bestowed Stl when amplified
from the MO34 genome and transformed into a Stl recipient.
Similar transformation and sequencing experiments were performed using
PCR fragments generated from strain MO38 (stl6). These
experiments found that the stl6 allele caused the identical
D796G substitution. Thus two independently isolated stl alleles targeted the same ` residue. We conclude that the
D796G substitution alone is sufficient to confer Stlin
vivo. Notably, B. subtilis residue D796 lies in the
C-terminal portion of Region F, one of the eight regions that are
conserved among the largest subunits of eukaryotic RNA polymerases and E. coli `(28) .`, E. coli `, and representative eukaryotic homologues. Significantly,
the available evidence indicates that Region F is important for
transcriptional elongation in both prokaryotic and eukaryotic cells.
Among eukaryotes, all known alterations that enhance resistance to the
fungal toxin -amanitin are found in or immediately adjacent to
Region F (see (29) and references therein). -Amanitin
binds directly to RNA polymerase II and inhibits both transcriptional
initiation and elongation, slowing phosphodiester bond formation and
translocation by an as yet unknown
mechanism(30, 31, 32, 33) . Among
prokaryotes, substitutions at 14 of the 85 residues in E. coli Region F are known to alter the termination properties of the
enzyme, and this consequence is thought to reflect the effects of these
substitutions on elongation kinetics (34) . Weilbaecher et
al.(34) advanced a possible explanation for these various
phenotypes; Region F might comprise part of a site that binds either
the 3` end of the nascent transcript or the new DNA template as it
directs incorporation of incoming nucleotides, and disruption of either
of these activities would inhibit the elongation reaction.
`
sequence (Ec) are from Jokerst et al.(28) ;
the B. subtilis ` sequence (Bs) is from this
study. Residues identical to the Drosophila IIa sequence are
indicated by colons (:), whereas substitutions are indicated
by a lowercase letter. Gaps introduced into the prokaryotic
sequences to improve the alignment are shown by dashed lines.
Because there is additional strong conservation between B. subtilis and E. coli `, identity between the B. subtilis and E. coli subunits is indicated by periods (.). The arrow above the B. subtilis sequence
denotes the D796G substitution, which confers Stlin
vivo. The similar arrow at the adjacent E. coli residue denotes the S793F substitution(14) , which confers
Stlin vitro and in vivo. E. coli residues at which single substitutions cause altered termination
phenotypes (34) are indicated by carets () below the E. coli sequence. Eukaryotic residues at which single
substitutions yield
-amanitin resistance are indicated by asterisks above the Drosophila IIa
sequence(29) .
alteration we mapped in Region F of B. subtilis `, Severinov and colleagues identified three alterations to
Region F of E. coli ` that confer Stlin
vitro(14) . One of these, S793F, targets the residue that
corresponds to S797 in B. subtilis and lies immediately
adjacent to the B. subtilis D796G alteration we mapped (see Fig. 2). The other two, M747I and R780H, are from the collection
of termination-altering mutants selected by Weilbaecher et al.(34) and confer only weak Stl. Stl in
prokaryotes might be considered the functional analog of -amanitin
in eukaryotes, in that both molecules affect transcription initiation
and elongation primarily by interfering with the elongation reaction.
If this is the case, then the similar location of alterations
conferring Stl in organisms as evolutionarily diverse as B. subtilis and E. coli provides further evidence for
the importance of Region F in the elongation reaction of RNA
polymerases from all organisms.Stl
In E. coli Mutations Also Map in the Conserved
rif Region of rpoB, a number of
substitution, deletions, and insertions in the region between Rif
clusters I and II were found to confer
Stl(6, 9) . Further extensive mutagenesis
found that single substitutions conferring Stl were
confined to the four contiguous residues 543-546(10) ,
which correspond to residues 499-502 of B. subtilis (13) . Because the sequences of the two Rif clusters
and the intervening spacer regions are so similar in the two species (Fig. 3), it was reasonable to expect that alterations in
residues 499-502 of B. subtilis would also lead to
Stl.
subunits. The sequence of B.
subtilis is from (13) and that of E. coli from (35) . Residues identical to the B.
subtilis subunit are indicated by periods (.) and
substitutions by lowercase letters. The locations of Rif
clusters I and II are shown underlined(7, 8, 9) . In E.
coli, the four residues in the intervening spacer region that are
the site of substitutions conferring Stl(10) are
shown in larger type (residues 543-546). In B.
subtilis, we made the corresponding substitutions (residues
499-502) and found that A499V, G500R, and E502V elicited
Stlin vivo.
transformants at a frequency significantly greater (10-fold) than the
control plasmid, which bore the corresponding wild-type region. In
contrast, plasmids bearing the M501S and (499-502)
alterations failed to yield significant numbers of Stl
transformants. Direct sequencing of the chromosome of representative
Stl strains verified that each of the alterations, A499V,
G500R, and E502V, was the only change that had been introduced into the rpoB region. To determine whether the A499V, G500R, and E502V
alterations were sufficient to confer Stlin vivo,
the region containing each was amplified from the appropriate Stl strain by PCR, sequenced to confirm the fidelity of the
amplification, then transformed a second time into a Stl recipient. The high frequency of Stl transformants
obtained verified that each alteration was indeed sufficient. Thus
M501S was the only substitution that did not lead to Stl,
and M501 occupies the only position that is not exactly conserved
between the Stl regions of B. subtilis and E. coli (Fig. 3).: 3 µg/ml for wild
type, 20 µg/ml for A499V, 10 µg/ml for G500R, and 50 µg/ml
for E502V. We compared the resistances imparted by equivalent changes
to each of the four contiguous positions in B. subtilis and E. coli (see Fig. 3). Counting from the
N-terminal end of each four-residue region, in B. subtilis the
lowest in vivo resistance was imparted by the second
substitution, G500R, and the highest by the fourth, E502V. In contrast,
the highest resistances in E. coli were associated with
the second and third substitutions, G544R and F545S(10) . mutants from the M501S and
(499-502) plasmids leads us to speculate that M501 plays a
more critical role in function than the other three residues, and
that alterations at position 501 are therefore proscribed in B.
subtilis . In accord with this notion, the F545S substitution
of the corresponding residue in E. coli caused slower
elongation kinetics in a P
-t pausing
assay when compared to enzyme containing either wild type
or a
subunit bearing A543V(10) ., the A499V, G500R, and E502V substitutions did not
noticeably affect the function of RNA polymerase in vivo.
Strains bearing these substitutions were indistinguishable from wild
type with regard to growth rate, sporulation frequency, and temperature
range (data not shown). Therefore, as a practical matter, the new
Stl alterations we constructed in B. subtilis rpoB furnish neutral genetic markers for the analysis of
function, in marked contrast to the available Rif alterations in rpoB which often cause highly pleiotropic
phenotypes (see Refs. 8, 13, 36, and 37). Similarly, the availability
of a well characterized Stl marker within B. subtilis
rpoC should facilitate analysis of ` function.Do
Based on the available data, Weilbaecher et al.(34) proposed a speculative model in which the and ` Interact to Form a Single Stl Binding
Site? and
` subunits join to form a symmetrical scaffold and catalytic
center that directs RNA synthesis from double-stranded DNA templates.
In light of this model, one interpretation of our results is that the
Stl target residues in and Region F in ` together form a
single Stl binding site, which overlaps a catalytic domain important in
transcription elongation. In this view, Stl binding could to be
prevented by changing a key contact on either or `. There
are three lines of evidence in support of this interpretation. First,
studies of elongation kinetics in the presence of Stl are consistent
with a single site of interaction between the antibiotic and the
eubacterial core enzyme(5) . Second, in both prokaryotic and
eukaryotic systems, there is ample evidence which suggests that regions
homologous to the putative Stl target in B. subtilis `
are important in transcription
elongation(29, 30, 31, 32, 33, 34) .
And third, the putative Stl target region in E. coli ,
although itself dispensable(9, 10) , nonetheless lies
immediately adjacent to regions implicated in nucleotide binding and
transcription elongation(8, 38) .
), resistant or resistance; PCR, polymerase chain reaction.
We thank Konstantin Severinov and colleagues for
communicating results prior to publication, Laura Heisler and Carol
Gross for their generous gift of streptolydigin, A. L. Sonenshein for
providing strains MO34 and MO38, and Michele Igo for helpful comments
on the manuscript.
©1995 by The American Society for Biochemistry and Molecular Biology, Inc.
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K. Severinov, A. Mustaev, A. Kukarin, O. Muzzin, I. Bass, S. A. Darst, and A. Goldfarb Structural Modules of the Large Subunits of RNA Polymerase. INTRODUCING ARCHAEBACTERIAL AND CHLOROPLAST SPLIT SITES IN THE beta AND beta prime SUBUNITS OF ESCHERICHIA COLI RNA POLYMERASE J. Biol. Chem., November 1, 1996; 271(44): 27969 - 27974. [Abstract] [Full Text] [PDF]
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M. D. Rudd and D. S. Luse Amanitin Greatly Reduces the Rate of Transcription by RNA Polymerase II Ternary Complexes but Fails to Inhibit Some Transcript Cleavage Modes J. Biol. Chem., August 30, 1996; 271(35): 21549 - 21558. [Abstract] [Full Text] [PDF]
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K. Severinov, D. Markov, E. Severinova, V. Nikiforov, R. Landick, S. A. Darst, and A. Goldfarb Streptolydigin-resistant Mutants in an Evolutionarily Conserved Region of the beta` Subunit of Escherichia coli RNA Polymerase J. Biol. Chem., October 13, 1995; 270(41): 23926 - 23929. [Abstract] [Full Text] [PDF]
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M. Hamada, A. L. Sakulich, S. B. Koduru, and R. J. Maraia Transcription Termination by RNA Polymerase III in Fission Yeast. A GENETIC AND BIOCHEMICALLY TRACTABLE MODEL SYSTEM J. Biol. Chem., September 8, 2000; 275(37): 29076 - 29081. [Abstract] [Full Text] [PDF]
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