Functional recognition of fragmented operator sites by R17/MS2 coat protein, a translational repressor.
The R17/MS2 coat protein serves as a translational repressor of replicase by binding to a 19 nt RNA hairpin containing the Shine-Dalgarno sequence and the initiation codon of the replicase gene. We have explored the structural features of the RNA operator site that are necessary for efficient translational repression by the R17/MS2 coat protein in vivo . The R17/MS2 coat protein efficiently directs lysogen formation for P22 R17 , a bacteriophage P22 derivative that carries the R17/MS2 RNA operator site within the P22 phage ant mRNA. Phages were constructed that contain fragmented operator sites such that the Shine-Dalgarno sequence and the initiation codon of the affected gene are not located within the RNA hairpin. The wild-type coat protein directs efficient lysogen formation for P22 phages that carry several fragmented RNA operator sites, including one in which the Shine-Dalgarno sequence is positioned 4 nt outside the coat protein binding site. Neither the wild-type R17/MS2 coat protein nor super-repressor mutants induce lysogen formation for a P22 phage encoding an RNA hairpin at a distance of 9 nt from the Shine-Dalgarno sequence, implying that a discrete region of biological repression is defined by the coat protein-RNA hairpin interaction. The assembly of RNA species into capsid structures is not an efficient means whereby the coat protein achieves translational repression of target mRNA transcripts. The R17/MS2 coat protein exerts translational regulation that extends considerably beyond the natural biological RNA operator site structure; however, the coat protein still mediates repression in these constructs by preventing ribosome access to linear sequence determinants of the translational initiation region by the formation of a stable RNA secondary structure. An efficient translational regulatory mechanism in bacteria appears to reside in the ability of proteins to regulate RNA folding states for host cell and phage mRNAs.
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Department of Microbiology and College of Medicine, University of Illinois at Urbana-Champaign, B103 Chemical and Life Sciences Laboratory, 601 South Goodwin Avenue, Urbana, IL 61801, USA.
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D017100:Bacteriophage P22 / Q000235:genetics; D001665:Binding Sites; D002213:Capsid / Q000378:metabolism*; D036022:Capsid Proteins; D015967:Gene Expression Regulation, Viral; D009690:Nucleic Acid Conformation; D009875:Operator Regions, Genetic; D014176:Protein Biosynthesis; D012367:RNA, Viral / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism*; D012324:RNA-Dependent RNA Polymerase / Q000037:antagonists & inhibitors; D012097:Repressor Proteins / Q000378:metabolism*; D014764:Viral Proteins
D036022:Capsid Proteins; C034261:P22 repressor protein, Enterobacteria phage P22; D012367:RNA, Viral; D016601:RNA-Binding Proteins; D012097:Repressor Proteins; D014764:Viral Proteins; D012324:RNA-Dependent RNA Polymerase