INHIBITION OF ESCHERICHIA-COLI RNA-POLYMERASE BY BACTERIOPHAGE-T4 ASIA

The 10 kDa bacteriophage T4 antisigma protein AsiA binds the Escherich ia coli RNA polymerase promoter specificity subunit, sigma(70), with h igh affinity and inhibits its transcription activity. AsiA binds to si gma(70) primarily through an interaction with sigma(70) conserved regi on 4.2, which has also been implicated in sequence-specific recognitio n of the -35 consensus promoter element. Here we show that AsiA forms a stable ternary complex with core RNA polymerase (RNAP) and sigma(70) and thus does not inhibit sigma(70) activity by preventing its bindin g to core RNAP. We investigated the effect of AsiA on open promoter co mplex formation and abortive initiation at two -10/-35 type promoters and two ''extended -10'' promoters. Our results indicate that the bind ing of AsiA to sigma(70) and the interaction of sigma(70) region 4.2 w ith the -35 consensus promoter element of -10/-35 promoters is mutuall y exclusive. In contrast, AsiA has much less effect on open promoter c omplex formation and abortive initiation from extended -10 promoters, which lack a -35 consensus element and do not require sigma(70) conser ved region 4.2. From these results we conclude that T4 AsiA inhibits E . coli RNAP sigma(70) holoenzyme transcription at -10/-35 promoters by interfering with the required interaction between sigma(70) conserved region 4.2 and the -35 consensus promoter element. (C) 1998 Academic Press Limited.