BLOCKING OF THE INITIATION-TO-ELONGATION TRANSITION BY A TRANSDOMINANT RNA-POLYMERASE MUTATION

RNA polymerase, the principal enzyme of gene expression, possesses structural features conserved in evolution. A substitution of an evolutionarily invariant amino acid (Lys1065 -→Arg) in the β subunit of Escherichia coli RNA porymerase apparently disrupts its catalytic center. The mutant protein inhibited cell growth when expressed from an inducible promoter. The assembled holoenzyme carrying the mutant subunit formed stable promoter complexes that continuously synthesized promoter-specific dinucleotides but that did not enter the elongation step. The mutant porymerase inhibited transcription by blocking the access of the wild-type enzyme to promoters.