PsiB, and anti-SOS protein, is transiently expressed by the F sex factor during its transmission to an Escherichia coli K-12 recipient.
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 plasmids: the latter type produces a detectable level of PsiB protein while the former does not. The discrepancy can be assigned to a Tn10 out-going promoter located upstream of psiB. When we inserted a Tn10 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+ x 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 plasmid 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 phenotype.
Bagdasarian
M
M
Michigan Biotechnology Institute, Lansing 48909.
Bailone
A
A
Angulo
J F
JF
Scholz
P
P
Bagdasarian
M
M
Devoret
R
R
D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D003227:Conjugation, Genetic; D004251:DNA Transposable Elements; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D005144:F Factor; D015870:Gene Expression; D015183:Restriction Mapping; D013014:SOS Response, Genetics; D015053:Zygote
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; C058074:PsiB protein, Bacteria