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J. Biol. Chem., Vol. 277, Issue 21, 18665-18669, May 24, 2002

This Article Abstract Full Text (PDF) All Versions of this Article: 277/21/18665    most recent M201033200v1 Submit a Letter to Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Katz, Y. S. Articles by Danon, A. Search for Related Content PubMed PubMed Citation Articles by Katz, Y. S. Articles by Danon, A. Social Bookmarking                      What's this?

The 3'-Untranslated Region of Chloroplast psbA mRNA Stabilizes Binding of Regulatory Proteins to the Leader of the Message^*

Yael S. Katz and Avihai Danon^§

From the Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel

Received for publication, January 31, 2002

	ABSTRACT

TOP ABSTRACT INTRODUCTION EXPERIMENTAL PROCEDURES RESULTS DISCUSSION REFERENCES

The 5'-leader and 3'-tail of chloroplast mRNAs have been suggested to play a role in posttranscriptional regulation of expression of the message. The regulation is thought to be mediated, at least in part, by regulatory proteins that are encoded by the nuclear genome and targeted to the chloroplast where they interact with chloroplast mRNAs. Previous studies identified high affinity binding of the 5'-untranslated region (UTR) of the chloroplast psbA mRNA by Chlamydomonas reinhardtii proteins. Here we tested whether the 3'-UTR of psbA mRNA alone or linked in cis with the 5'-UTR of the mRNA affects the high affinity binding of the message in vitro. We did not detect high affinity binding that is unique to the 3'-UTR. However, we show that the cis-linked 3'-UTR increases the stability of the 5'-UTR binding complex. This effect could provide a means for translational discrimination against mRNAs that are incorrectly processed.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION EXPERIMENTAL PROCEDURES RESULTS DISCUSSION REFERENCES

In initiation of translation, ribosomes bind to the 5'-untranslated region (UTR)¹ of the mRNA and are consequently directed to the initiator codon of the open reading frame. The 5'-UTR of several chloroplast mRNAs in higher plants and in the unicellular green alga Chlamydomonas reinhardtii contain regions of inverted repeats and binding sites for nuclear encoded proteins. These interactions have been shown to be involved not only in regulation of translation but also in processing and stability of the message (1-10). It has been suggested that ribosome association at the 5'-UTR may couple translation with mRNA stability (11, 12). Most chloroplast mRNAs have an AU-rich 3'-UTR with a terminal inverted repeat. This 3'-UTR inverted repeat has been shown to play a role in the processing and stabilization of the mRNA (13-17). Identification of interactions between the two termini of cytoplasmic transcripts (18, 19) and examples of 3'-UTR modulation of translation initiation in both eukaryotes (18, 20) and prokaryotes (21-23) raise the possibility that interactions of the 5'- and 3'-UTR of chloroplast mRNAs may influence their expression. In support of this notion, recent results have shown that correct processing of the 3'-UTR can promote translation initiation and polysomal association (24).

Expression of the D1 protein, encoded by the chloroplast psbA mRNA, is a prime example of the regulation of translation involving the interaction of nuclear encoded factors and regions of inverted repeats in the 5'-UTR of the transcript (3, 6, 25-27). In C. reinhardtii, the 5'-UTR of psbA mRNA is the target for the light-regulated binding of a complex of proteins of 38, 47, 55, and 60 kDa (3). These proteins interact with an inverted repeat that is located upstream from a potential Shine-Dalgarno-like site in the 5'-UTR (3, 7) and possibly with a second site after psbA mRNA undergoes 5'-processing (28). Assays of D1 synthesis in C. reinhardtii mutants, in which the inverted repeat has been partially deleted or mutated, indicate the importance of the stem-loop fold for the light-responsive increase of D1 synthesis (7).

The central RNA-binding protein in the psbA 5'-binding complex is the 47-kDa protein (RB47). RB47 is a nuclear encoded protein that shows high homology to poly(A)-binding proteins (29). Mutants in which RB47 expression is low or lacking are defective in D1 translation, implicating RB47 as a message-specific translational factor (29-31). The 60-kDa protein (RB60) is a protein-disulfide isomerase-like protein also encoded by the nuclear genome (32). RB60 has been identified as the regulatory redox-active protein of the psbA 5'-binding complex and is the likely candidate for perceiving the light-signal and modulating the binding of the complex (33).

In addressing the potential modes of regulation of psbA expression, we examined whether the 3'-UTR affects protein binding to psbA mRNA. We report here a comparison of binding of C. reinhardtii proteins to RNA probes of 5'-UTR, 3'-UTR, and cis-linked 5'-UTR-3'-UTR. Our analysis indicated that the high affinity binding to psbA mRNA is primarily via its 5'-UTR, whereas the presence of 3'-UTR in cis increases the affinity of binding of the 5'-UTR-binding protein complex.

	EXPERIMENTAL PROCEDURES

TOP ABSTRACT INTRODUCTION EXPERIMENTAL PROCEDURES RESULTS DISCUSSION REFERENCES

psbA RNA Constructs-- To assess the influence of psbA 3'-UTR on binding of the psbA 5'-binding complex, five types of RNA probes containing the psbA UTRs were constructed as shown in Fig. 1. The 5' transcript (5'-T) included the 5'-UTR and 36 bp downstream of the initiator codon, and the 3' transcript (3'-T) contained 30 bp preceding the stop codon and the 3'-UTR. The fused 5'-UTR and 3'-UTR transcript (5'3'-T) was composed of the combined 5'-T and 3'-T, in "sense" orientation. The 5'3'-NC-T transcript lacked the 30-bp coding region proximal to the 3'-UTR and the 5'3'-LC-T transcript included a longer segment of the 3'-coding region (Fig. 1). The psbA UTR constructs were verified by sequence analysis.

View larger version (18K): [in this window] [in a new window]   Fig. 1.   Schematic representation of the three expression constructs used for in vitro transcription. The 92 bp of the psbA 5'-UTR (light gray box) and 36 bp from the coding region (white box) were subcloned under the T7 promoter to form the 5' transcript (5'-T). The 52 bp of 3'-UTR (dark gray box) and 30 bp of upstream coding region (hatch box) were subcloned to form the 3' transcript (3'-T). Fusion in sense orientation of the 5'-T and 3'-T created the 5'3'-T transcript (5'3'-T). The 5'3'-NC-T transcript (5'3' NC-T) lacked the 30-bp coding region proximal to the 3'-UTR, and the 5'3'-LC-T transcript (5'3' LC-T) included a longer segment of the 3'-coding region. SacI, XbaI, AccI, and BamHI denote restriction sites used for building the constructs.

Algae Growth Conditions and Purification of RNA-binding Proteins-- C. reinhardtii 2137a cells were grown in TAP medium (34), under continuous light at 25 °C, to a density of ~1 × 10⁷ cells/ml. The C. reinhardtii proteins were enriched for RNA-binding proteins by liquid chromatography using a heparin-agarose column (3). Bound proteins were eluted from the column with a potassium acetate gradient of 0.1-1.6 M (3). The recombinant RB47 protein (rRB47) containing a His₆ tag at its amino terminus was produced in Escherichia coli and purified on a Ni-His trap column.

In Vitro Transcription, Gel Mobility Shift, and UV-cross-linking Assays-- Each of the plasmids containing the psbA UTRs was digested with either XbaI or BamHI restriction enzyme and used as a template in run-off transcription reactions containing [³²P]UTP (3). Purified radiolabeled RNA probes were used in gel mobility shift (GMS) assays to compare the binding of the psbA 5', 3'- or 5'-3'-UTR RNA to proteins extracted from C. reinhardtii.

In GMS experiments, the proteins were first incubated, at room temperature, with 15 units of Prime-RNase inhibitor in 10 µl of buffer containing 20 mM Tris (pH 7.5), 100 mM potassium acetate, 0.2 mM EDTA, 5 mM -mercaptoethanol, 4.5 mM MgCl₂, 1.5 mM dithiothreitol, and 20% glycerol. Next, the proteins were incubated with the ³²P-labeled RNA transcripts and, where specified, with nonlabeled RNA competitors. Nonspecific RNA competitors that included 20 µg of tRNA (Sigma) and 2 µg of total RNA isolated from a mutant cell line of C. reinhardtii that lacks the psbA gene (FuD7) were included in both GMS and UV-cross-linking assays. The products of GMS assays were separated on 5% native polyacrylamide gels (3), and formation of RNA-protein complexes was visualized by autoradiography or by phosphorimaging.

In the UV-cross-linking assays, ³²P-labeled RNA-protein complexes were placed, on ice, 5 cm from the lamps of a Stratalinker device and irradiated for 30 min. The RNA transcripts were digested with 50 µg of RNase A (Sigma) for 30 min in the presence of 3 M urea, 3 mM EDTA at 55 °C. After adding SDS and -mercaptoethanol to 2.5% final concentrations, proteins were fractionated by 12% SDS-PAGE (35), and radiolabeled proteins were detected by autoradiography.

	RESULTS

TOP ABSTRACT INTRODUCTION EXPERIMENTAL PROCEDURES RESULTS DISCUSSION REFERENCES

C. reinhardtii Proteins Exhibit High Affinity Binding to cis-linked UTRs-- C. reinhardtiiproteins partially purified by heparin affinity chromatography were incubated with ³²P-labeled 5'-T transcript and subjected to GMS assay. Total RNA, extracted from the C. reinhardtii mutant cell line (FuD7) lacking the psbA gene, was included in the binding reactions to compete out binding that was not psbA mRNA-specific. Protein fractions, previously shown to contain the 47- and 60-kDa proteins (3), demonstrated prominent binding activity to the 5'-UTR of psbA mRNA as expected (Fig. 2A). When the same protein fractions were incubated with an equimolar concentration of ³²P-labeled 3'-T transcript, only faint binding was observed (Fig. 2B). This suggests that the protein(s) binding to the 3'-UTR are either much less abundant or have significantly lower affinity than those that bind the 5'-UTR.

View larger version (49K): [in this window] [in a new window]   Fig. 2.   Gel mobility assays showing binding of C. reinhardtii proteins to the three psbA transcripts. Protein fractions from heparin affinity chromatography were incubated with radiolabeled 5'-T (A), 3'-T (B), 5'3'-T (C), 5'3'-NC-T (D), or 5'3'-LC-T (E) RNAs, in the presence of non-labeled tRNA and FuD7 RNA, and subjected to GMS assay. Fractions 14 and 15 contain high affinity binding activity to 5'-T and 5'3'-T. Fractions 10-12 have RNase activity that causes degradation of the free RNA probe. Longer incubation periods of radiolabeled RNA and Fractions 14 and 15 prior to GMS assays verified lack of RNase activity in these fractions (data not shown). RNA denotes sample containing the labeled RNA transcript without protein. Column fractions represent samples containing C. reinhardtii proteins of the indicated fractions of heparin column chromatography. Complex and Free mark the mobility of the RNA-protein complex and the free RNA, respectively.

Interestingly, a notably high binding signal was detected when concentration of an equimolar ³²P-labeled 5'3'-T transcript was included in the GMS assay (Fig. 2C). This result implies that the presence in cis of the 3' terminus of the message resulted in formation of a higher affinity protein-RNA complex. To establish whether this phenomenon is caused by the 3'-UTR or is unique to the 5'3'-T, two additional 5'3' transcripts, 5'3'-NC-T (with no 3'-proximal coding region) and 5'3'-LC-T (with long 3'-proximal coding region), were tested (Fig. 2, D and E). These two 5'3' transcripts also caused stabilization of the complex in comparison with the 5'-T, assigning a primary role to the 3'-UTR in this phenomenon. These results suggested three main alternatives: 1) the presence in cis of 3'-UTR in the 5'3'-T transcript increases the affinity of the 5'-UTR binding activity; 2) the presence in cis of 5'-UTR increases the affinity of a novel binding to the 3'-UTR; 3) a novel binding activity with high specificity to the 5'3'-T was detected in the GMS assay. To differentiate between these alternatives the following experiments were performed.

Binding of cis-linked UTRs Is via RB47-- In a UV-cross-linking (UVCL) assay, a radioactive label is transferred from the RNA to the protein(s) that comes into close contact with the RNA molecule. The labeled protein is then identified by autoradiography of SDS-PAGE-fractionated proteins. We reasoned that if the high binding activity observed with the 5'3'-T transcript is due to a novel binding protein, specific either to the 3'-UTR or to the cis-linked 5'3'-T transcript, then the UVCL assay might detect it. UVCL assay with ³²P-labeled 5'-T transcript, in the presence of tRNA and FuD7 total RNA as competitors, typically labeled the RB47 protein (Fig. 3A).

View larger version (23K): [in this window] [in a new window]   Fig. 3.   UVCL assay showing binding of C. reinhardtii proteins to the three transcripts. Protein fractions from heparin affinity chromatography (column fractions) were incubated with radiolabeled 5'-T (A), 3'-T (B), or 5'3'-T (C), in the presence of non-labeled tRNA and FuD7 RNA and subjected to UVCL assay. The pattern of radiolabeled proteins is similar for the 5'-T and 5'3'-T, with a primary label transfer to a 47-kDa protein (RB47) from fractions 14 and 15.

In agreement with the results of the GMS analysis, only a faint signal corresponding to the 47-kDa protein was detected with ³²P-labeled 3'-T transcript in the UVCL assay (Fig. 3B). The pattern of proteins labeled by cross-linking to the 5'- or 5'-3'-RNA was similar (Fig. 3, A and C). There was no notable difference of protein bands to account for the influence of the 3'-UTR on the 5'3'-T binding in GMS assays. However, this does not exclude binding that may occur in an RNA region that does not have enough uridine bases to cause strong labeling of the protein(s) or protein-protein interactions that may affect the RNA binding. These results suggest that the binding to the 5'3'-T is also by RB47 and its associated proteins and mainly via the 5'-UTR. To confirm this, the specificity of the binding to the transcripts was addressed further using affinity and competition assays.

Specificity and Affinity of cis-linked UTR Binding Activity-- In competition assays, the specificity of RNA binding is evaluated by including increasing amounts of non-labeled competitor RNAs in the binding reactions. A higher capacity of a non-labeled RNA to compete with the radioactive RNA for the binding activity ranks it higher in specificity. If the binding to the transcript containing the cis-linked 5'- and 3'-UTRs is principally via the 5'-UTR, then this RNA should compete better than the 3'-UTR. To assess the specificity of binding to the 5'3'-T RNA, GMS assays containing either the ³²P-labeled 5'-T transcript or the 5'3'-T transcript were performed in the presence of 5-, 25-, 50-, 100-, 200-, and 400-fold excess of non-labeled 5'-T or 3'-T RNAs (Fig. 4A). The non-labeled 5'-UTR transcript competed with the radiolabeled 5'-T or 5'3'-T RNAs. In contrast, the 3'-UTR did not effectively compete with binding of either the 5'-UTR or 5'3'-T transcript. Similar results were obtained when 5'-T or 3'-T competitors were included in UVCL assays (Fig. 4B). These results show that specificity of RB47 protein and its associated proteins is primarily to the 5'-UTR, rather than the 3'-UTR, and strongly argue for its binding the 5'3'-T transcript mainly via the segment containing the 5'-UTR.

View larger version (75K): [in this window] [in a new window]   Fig. 4.   Specificity of binding of 5'-UTR and 5'3'-T. Comparison of the competition by non-labeled 5'- or 3'-RNA transcripts was analyzed by GMS assay performed with radiolabeled 5'-T or 5'3'-T (A). Minimal protein concentrations required for complex formation with each of the 5'-T and 5'3'-T transcripts were used as determined in Fig. 5 (a 3-fold higher protein concentration in 5'-T assays than in 5'3'-T assays). Non-labeled 5'-T competed effectively for the binding of C. reinhardtii proteins, whereas 3'-T did not. Native complex and Free mark the mobility of the native RNA-protein complex and the free RNA, respectively. Competition assays performed in a UV-cross-linking assay (B) also demonstrated that the 5'-T, but not the 3'-T, effectively competed for RB47 labeling.

If RB47 and its associated proteins bind the psbA 5'-UTR segment of 5'-T and 5'3'-T RNAs then what is the mechanism for enhanced binding of 5'3'-T? One possibility is that the cis-linked 3'-UTR increases the affinity of the native protein complex to the RNA. To compare the affinity of 5'-T and 5'3'-T binding, decreasing amounts of C. reinhardtii proteins were mixed with equimolar concentrations of each type of RNA and subjected to GMS assay. The results in Fig. 5 show that an ~3-fold lower concentration of proteins, containing an estimated concentration of 0.07 µM RB47, was required for 50% native complex formation with the radiolabeled 5'3'-T RNA than with the 5'-UTR alone. This shows that the RB47 and its associated proteins bind the 5'3'-T with higher affinity than the 5'-T alone. Therefore, although the 3'-UTR itself exhibits only minor protein binding in GMS or UVCL assays, its fusion to the 5'-UTR seems to stimulate the binding of the native protein complex.

View larger version (36K): [in this window] [in a new window]   Fig. 5.   Affinity of 5'-UTR and cis-linked UTR binding activities. The protein concentration that resulted in 50% binding of either the 5'-UTR (A) or the cis-linked 5'-3'-UTRs (B) was determined by incubating each radiolabeled RNA with decreasing amounts of C. reinhardtii proteins and analyzing the formation of protein-RNA complexes by GMS assay. The combined results of three independent experiments are presented in a graph (C). Approximately 3-fold higher concentrations of proteins were required for 50% binding of the native complex to 5'-T than to 5'3'-T. RNA denotes sample containing the labeled RNA transcript without protein. µg protein represents samples containing C. reinhardtii proteins of Fraction 14 of heparin column chromatography. Native complex and Free mark the mobility of the native RNA-protein complex and the free RNA, respectively.

rRB47 Does Not Bind the cis-linked UTRs with Preferential Affinity-- RB47 was the primary binding protein identified in assays containing 5'-T and 5'3'-T RNAs. To determine whether binding of RB47 on its own is sufficient for the preferential affinity to the cis-linked transcript, we assayed whether purified recombinant RB47 (rRB47) can mimic the binding of the native complex containing RB47 in GMS assays. Binding of rRB47 to 5'-T or 5'3'-T formed complexes that migrated faster than the corresponding native complex (Fig. 6A), suggesting that the complex formed by the intrinsic binding contained additional proteins. Further, in contrast to the preferential affinity of the native complex to the 5'3'-T, the binding of rRB47 to both 5'- and 5'3'-RNA is of similar affinity (Fig. 6, B and C). In fact, on its own rRB47 displayed a slight preference to the 5'-T (Fig. 6C), further supporting the different nature of binding of rRB47 and the native complex. Together, these results suggest that an additional protein(s) associated with RB47 is necessary for the preferential binding to the cis-linked 5'-3'-UTRs as compared with the 5'-UTR and that the presence in cis of the 3'-UTR promotes the binding of the native complex comprised of RB47 and its cognate proteins. We tested whether the inclusion of recombinant RB60 (rRB60) with rRB47 mimics the binding of the native complex. However, rRB60 and rRB47 together also did not result in preferential binding of the cis-linked 5'3'-T RNA (data not shown) suggesting that the addition of RB60 was either not required or not sufficient.

View larger version (39K): [in this window] [in a new window]   Fig. 6.   rRB47 binding to 5'-T and 5'3'-T transcripts. Comparison of the binding of recombinant RB47 (rRB47) to the 5'-T and 5'3'-T RNAs with binding of C. reinhardtii heparin column chromatography fraction 14 (Hep) by GMS assay (A). RNA denotes sample containing the labeled RNA transcript without protein. The affinity of rRB47 binding to the 5' of 5'-3'-RNA was examined by determining the concentration of rRB47 that results in 50% binding of either the 5'-T and 5'3'-T RNAs (B). The combined results of three independent experiments are presented in a graph (C). Binding of rRB47 to 5'-T and 5'3'-T transcripts displayed similar affinities. Native complex, rRB47 complex, and Free mark the mobility of the native RNA-protein complex, the RNA-rRB47 complex, and the free RNA, respectively.

	DISCUSSION

TOP ABSTRACT INTRODUCTION EXPERIMENTAL PROCEDURES RESULTS DISCUSSION REFERENCES

Here we show that the presence in cis of the 3'-UTR of psbA mRNA is required for high affinity binding of the native complex, containing the RB47 protein, to the 5'-UTR. Several modes of action could explain the effect of the 3'-UTR on the binding of the proteins to the 5'-UTR of psbA mRNA. A change in the affinity of an RNA-protein complex may result from a conformational shift in the RNA and/or from an altered binding of the protein. Our results, so far, do not exclude either possibility. The 3'-UTR of psbA mRNA may interact directly with the 5'-UTR of the message, thereby inducing it to form a structural motif with high affinity to the native complex containing RB47. Such long range RNA-RNA interactions have been found to affect translational efficiency in prokaryotes (22). It should be noted that the MFOLD computer program for RNA structure analysis (36) did not predict any such 5'-UTR-3'-UTR interactions (data not shown). Alternatively, because low affinity binding of RB47 to the 3'-UTR was also found (Fig. 3), it is possible that RB47 may bind both UTRs of psbA mRNA when they are present in cis. This may not be entirely surprising as the 3'-UTR is AU-rich, and RB47 shares high homology with poly(A)-binding proteins (31). In this scheme, the simultaneous binding of RB47 and its associated proteins to the 5'- and 3'-UTRs forms a high affinity complex (Fig. 2).

Previous characterization of the 5'-UTR binding activity by GMS, UVCL, and psbA RNA-affinity chromatography assays suggested that it is composed of four proteins (3). The UVCL assay, which labels proteins that are in direct contact with the RNA, showed that RB47 is the primary RNA-binding protein of the complex (Fig. 3 and Ref. 3), and cloning of RB47 showed that it contains RNA-binding domains (31). Extraction of the proteins that were complexed with the 5'-UTR of psbA mRNA in the GMS assay revealed that RB60 is also associated with the RNA, potentially via protein-protein interactions with RB47 (3). Based on these results, it was suggested that the complex contains four proteins of which only binding of RB47 and RB60 was resistant to the conditions of the GMS (3).

A comparison of mobility shift of 5'-T and 5'3'-T RNAs by either rRB47 or by the partially purified C. reinhardtii proteins showed that the native proteins form complexes with slower mobility (Fig. 6), further indicating that the native complex contains additional protein(s), such as RB60, RB38, or RB55. The higher affinity of the binding of the native complex to the cis-linked 5'- and 3'-UTRs than to the 5'-T transcript indicates that the presence in cis of the 3'-UTR promotes the binding of the native complex comprised of RB47 and its cognate proteins. Interestingly, the recombinant RB47 binds the 5'-T and the 5'3'-T at similar high affinities (compare Figs. 5 and 6), suggesting that the lower affinity of the native complex in the absence of the 3'-UTR is a result of action of the proteins associated with RB47.

The activity of the proteins that bind the 5'-UTR psbA mRNA correlates with the translation rate of the D1 protein in C. reinhardtii cells (3). Therefore, the increased affinity of 5'-UTR psbA mRNA-binding proteins conferred by the 3'-UTR may suggest that the 3'-UTR influences D1 synthesis by stimulating binding of the native complex, comprised of RB47 and its cognate proteins, to the 5'-UTR. Correct processing of the 3'-UTR was suggested to be required for high levels of translation initiation and polysomal association in C. reinhardtii cells (24). Recent results from tobacco transformants in which the influence of the psbA UTRs on translation of a reporter gene were studied indicated that including the psbA 3'-UTR resulted in a 3-4-fold enhancement of translation (25). In another study, deletion of the inverted repeat of the 3'-UTR of petD mRNA led to a reduction in petD expression beyond that expected by the decrease in mRNA accumulation alone, indicating that the 3'-UTR may also contribute to efficient translation (37). These findings suggest that the 3'-UTR of chloroplast messages is required for optimal translation, in addition to its role in determination of mRNA stability. Collectively, these results suggest that the impaired binding of the native complex, comprised of RB47 and its associated proteins, to a psbA mRNA lacking an intact 3'-UTR may discriminate it from efficient translation.

	FOOTNOTES

^* This work was supported by Grant 651/00 from the Israel Science Foundation and a grant from the Minerva Foundation.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Recipient of a Feinberg Graduate School Fellowship.

^§ Holder of the Judith and Martin Freedman Career Developmental Chair. To whom correspondence should be addressed. Tel.: 972-8-934-2382; Fax: 972-8-934-4181; E-mail: avihai.danon@weizmann.ac.il.

Published, JBC Papers in Press, March 19, 2002, DOI 10.1074/jbc.M201033200

	ABBREVIATIONS

The abbreviations used are: UTR, untranslated region; GMS, gel mobility shift; UVCL, UV-cross-linking; r, recombinant.

	REFERENCES

TOP ABSTRACT INTRODUCTION EXPERIMENTAL PROCEDURES RESULTS DISCUSSION REFERENCES

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This Article Abstract Full Text (PDF) All Versions of this Article: 277/21/18665    most recent M201033200v1 Submit a Letter to Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Katz, Y. S. Articles by Danon, A. Search for Related Content PubMed PubMed Citation Articles by Katz, Y. S. Articles by Danon, A. Social Bookmarking                      What's this?