Nucleic Acids Research, Vol 25, Issue 22 4464-4473, Copyright © 1997 by Oxford University Press
DE Fouts, HL True and DW Celander
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.
ARTICLES
Functional recognition of fragmented operator sites by R17/MS2 coat protein, a translational repressor
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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