Identification of psiB genes of plasmids F and R6-5. Molecular basis for psiB enhanced expression in plasmid R6-5. |
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| Authors: | M Dutreix A B?ckman J Célérier M M Bagdasarian S Sommer A Bailone R Devoret M Bagdasarian |
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| Institution: | GEMC, Enzymologie, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France. |
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| Abstract: | PsiB protein of plasmid R6-5 inhibits the induction of the SOS pathway. The F sex factor also carries a psiB gene homologous to that of R6-5. Yet, it fails to inhibit SOS induction. In order to solve this difference, we characterized the psiB genes of R6-5 and F. We found that (i) the sequences of the two psiB genes share extensive homology the predicted amino acid sequences of the two proteins differing by 5 residues, (ii) the expression of R6-5 psiB is 4 times higher than F psiB gene, (iii) in plasmid R6-5, a Tn10 transposon upstream from the psiB gene enhances psiB expression. Hence, the F sex factor may be unable to prevent SOS induction for two non-exclusive reasons: (i) F PsiB protein, being slightly different from R6-5, may be less active, (ii) the level of synthesis of F PsiB protein may be insufficient to prevent SOS induction. |
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