THE ESCHERICHIA-COLI DNA-REPAIR PROTEIN UVRA CAN RE-ASSOCIATE WITH THE UVRB - AFLATOXIN B-1-DNA COMPLEX IN-VITRO

The UvrA and UvrB proteins form part of the UVrABC endonuclease, which is responsible for nucleotide excision repair in Escherichia coli. Us ing a mobility shift gel assay we have studied the binding of UvrA dim er, UvrB monomer and UvrA(2)B trimer complexes with 40, 50 and 136 bp P-32-end-labelled DNA fragments adducted with aflatoxin B-1. UvrA was shown to re-associate with adduct specific UVrB:DNA complexes, a pheno menon which could be reversed by the addition of 500 mM potassium chlo ride or anti-UvrA anti-sera. Re-association was shown to be UvrA conce ntration dependent. Re-association of UvrA(2)B to the UvrB :DNA comple x was not seen. We have also shown that the UVrB:DNA complex, in the c ase of aflatoxin B-1, is extremely stable with a half-life in excess o f 400 min and that fragment termini are not a specific substrate for U vrA binding.