Abstract
We constructed hybrid Bordetella pertussis-Escherichia coli RNA polymerases and compared productive interactions between transcription activators and cognate RNA polymerase subunits in an in vitro transcription system. Virulence-associated genes of B. pertussis, in the presence of their activator BvgA, are transcribed by all variants of hybrid RNA polymerases, whereas transcription at the E. coli lac promoter regulated by the cyclic AMP-catabolite gene activator protein has an absolute requirement for the E. coli alpha subunit. This suggests that activator contact sites involve a high degree of selectivity.