P. Jonczyk et A. Nowicka, SPECIFIC IN-VIVO PROTEIN-PROTEIN INTERACTIONS BETWEEN ESCHERICHIA-COLI SOS MUTAGENESIS PROTEINS, Journal of bacteriology, 178(9), 1996, pp. 2580-2585
One of the components of the RecA-LexA-controlled SOS response in Esch
erichia coli cells is an inducible error-prone DNA replication pathway
that results in a substantial increase in the mutation rate. It is be
lieved that error-prone DNA synthesis is performed by a multiprotein c
omplex that is formed by UmuC, UmuD', RecA, and probably DNA polymeras
e III holoenzyme. It is postulated that the formation of such a comple
x requires specific interactions between these proteins. We have analy
zed the specific protein-protein interactions between UmuC, UmuD, and
UmuD' fusion proteins, using a Saccharomyces cerevisiae two-hybrid sys
tem. In agreement with previous in vitro data, we have shown that UmuD
and UmuD' are able to form both homodimers (UmuD-UmuD and UmuD'-UmuD'
) and a heterodimer (UmuD-UmuD'). Our data show that UmuC fusion prote
in is capable of interacting exclusively with UmuD' and not,vith UmuD.
Thus, posttranslational processing of UmuD into UmuD' is a critical s
tep in SOS mutagenesis, enabling only the latter protein to interact w
ith UmuC. Our data seem to indicate that the integrity of the entire U
muC sequence is essential for UmuC-UmuD' heterotypic interaction. Fina
lly, in our studies, we used three different UmuC mutant proteins: Umu
C25, UmuC36, and UmuC101. We have found that UmuC25 and UmuC36 are not
capable of associating with UmuD'. In contrast, UmuC104 protein inter
acts with UmuD' protein with an efficiency identical to that of the wi
ld-type protein. We postulate that UmuC104 protein might be defective
in interaction with another, unknown protein essential for the SOS mut
agenesis pathway.