Volume 270,
Number 21,
Issue of May 26, pp. 12794-12800, 1995
©1995 by The American Society for Biochemistry and Molecular Biology, Inc.
Distribution
of Cross-links between mRNA Analogues and 16 S rRNA in Escherichia
coli 70 S Ribosomes Made under Equilibrium Conditions and Their
Response to tRNA Binding
Dalia I.
Juzumiene
,
Tatjana G.
Shapkina
,
Paul
Wollenzien
The interaction between mRNA and Escherichia coli ribosomes has been studied by photochemical cross-linking using
mRNA analogues that contain 4-thiouridine (s
U) or
s
U modified with azidophenylacyl bromide (APAB), either two
nucleotides upstream or eight nucleotides downstream from the
nucleotide sequence ACC, the codon for tRNA
. The
sequences of the mRNA analogues were described earlier (Stade, K.,
Rinke-Appel, J., and Brimacombe, R.(1989) Nucleic Acids Res. 17, 9889-9908; Rinke-Appel, J., Stade, K., and Brimacombe,
R.(1991) EMBO J. 10, 2195-2202). Under equilibrium
conditions, both of these mRNA analogues bind and cross-link to 70 S
ribosomes without the presence of tRNA
; however, there
are significant increases both in binding and particularly in
cross-linking in the presence of the tRNA
. Four regions
contain cross-linking sites that increase in the presence of tRNA,
C
, A
, A
(and minor sites
around these three positions), and C
/U
.
Three other cross-linking sites, U
, A
, and
U
, show very little change in extent of cross-linking
when tRNA is present. A conformational change in the 30 S subunit
allowing additional accessibility to the 16 S rRNA by the mRNA
analogues upon tRNA binding best explains the behavior of the
tRNA-dependent and tRNA-independent mRNA-16 S rRNA cross-linking sites.