ISSN:
1365-2958
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
,
Medicine
Notes:
PsiB, an anti-SOS protein, shown previously to prevent activation of RecA protein, was purified from the crude extract of PsiB overproducing cells. PsiB is probably a tetrameric protein, whose subunit has a sequence-deduced molecular mass of 15741 daltons. Using an immuno-assay with anti-PsiB antibodies, we have monitored PsiB cell concentrations produced by F and R6-5 piasmids: the latter type produces a detectable level of PsiB protein while the former does not. The discrepancy can be assigned to a Tn 10 outgoing promoter located upstream of psiB. When we inserted a Tn 10 promoter upstream of F psiB, the F PsiB protein concentration reached the level of R6-5 PsiB.We describe here the physiological role that PsiB protein may have in the cell and how it causes an anti-SOS function. We observed that PsiB protein was transiently expressed by a wild-type F sex factor during its transmission to an Escherichia coli K-12 recipient, In an F+× F- cross, PsiB concentration increased at least 10-fold in F- recipient bacteria after 90 minutes and declined thereafter; the psiB gene may be repressed when F plasm id replicates vegetatively. PsiB protein may be induced zygotically so as to protect F single-stranded DNA transferred upon conjugation. PsiB protein, when overproduced, may interfere with RecA protein at chromosomal single-stranded DNA sites generated by discontinuous DNA replication, thus causing an SOS inhibitory pheno-type.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-2958.1992.tb01539.x
