INTERACTION OF BACTERIOPHAGE-T4 ASIA PROTEIN WITH ESCHERICHIA-COLI SIGMA(70) AND ITS VARIANT

Bacteriophage T4 produces a small protein AsiA, which inhibits transcr iption from sigma(70)-dependent promoters in E. coli by tightly bindin g to sigma(70) and is therefore termed as anti-sigma factor. We observ ed that there was no inhibition of single round transcription at lac U V5 promoter when AsiA was added to preformed open complex between RNA polymerase and template DNA. However, transcription was found to proce ed normally at 'extended -10' promoters in the presence of AsiA. It ap pears therefore that AsiA binds sigma(70) at its 4.2-subdomain or in i ts close vicinity. Further experiments on immunoprecipitation of sigma (70) and a mutant sigma(70)-V576G with AsiA seem to corroborate such c onclusion. (C) 1997 Federation of European Biochemical Societies.