RecA-mediated cleavage activates UmuD for mutagenesis: mechanistic relationship between transcriptional derepression and posttranslational activation.
The products of the SOS-regulated umuDC operon are required for most UV and chemical mutagenesis in Escherichia coli. It has been shown that the UmuD protein shares homology with LexA, the repressor of the SOS genes. In this paper we describe a series of genetic experiments that indicate that the purpose of RecA-mediated cleavage of UmuD at its bond between Cys-24 and Gly-25 is to activate UmuD for its role in mutagenesis and that the COOH-terminal fragment of UmuD is necessary and sufficient for the role of UmuD in UV mutagenesis. Other genetic experiments are presented that (i) support the hypothesis that the primary role of Ser-60 in UmuD function is to act as a nucleophile in the RecA-mediated cleavage reaction and (ii) raise the possibility that RecA has a third role in UV mutagenesis besides mediating the cleavage of LexA and UmuD.
Nohmi
T
T
Biology Department, Massachusetts Institute of Technology, Cambridge 02139.
Battista
J R
JR
Dodson
L A
LA
Walker
G C
GC
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004249:DNA Damage; D004269:DNA, Bacterial / Q000032:analysis; D004259:DNA-Directed DNA Polymerase; D004926:Escherichia coli / Q000187:drug effects / Q000528:radiation effects; D029968:Escherichia coli Proteins; D009154:Mutation; D010446:Peptide Fragments / Q000032:analysis; D010957:Plasmids; D011499:Protein Processing, Post-Translational; D011938:Rec A Recombinases / Q000494:pharmacology*; D014158:Transcription, Genetic; D014466:Ultraviolet Rays
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D010446:Peptide Fragments; D011938:Rec A Recombinases; D004259:DNA-Directed DNA Polymerase; C055218:UmuD protein, E coli