A COMMON ROLE OF CRP IN TRANSCRIPTION ACTIVATION - CRP ACTS TRANSIENTLY TO STIMULATE EVENTS LEADING TO OPEN COMPLEX-FORMATION AT A DIVERSE SET OF PROMOTERS

We have shown previously that the cyclic AMP receptor protein (CRP) is not required after the formation of the open complex at the lac promo ter (Tagami and Aiba, 1995, Nucleic Acids Res., 19, 6705-6712), In thi s paper, we investigate the role of CRP in transcription activation at the malT and gal promoters, At the malT promoter, RNA polymerase (RNA P) forms a nonproductive RNAP-promoter binary complex in the absence o f CRP and a productive CRP-RNAP-promoter ternary complex in the presen ce of CRP, CRP can be removed from the malT ternary complex by a moder ate concentration of heparin, The resulting binary complex is function ally identical to the ternary complex, At the gal promoter, RNAP predo minantly forms a binary complex at the P2 promoter in the absence of C RP and a ternary complex at the PI promoter in the presence of CRP, A very high concentration of heparin is able to dissociate CRP from the galP1 ternary complex without changing the properties of the complex, These data indicate that CRP is not required for the maintenance of th e ternary complex and plays no role in the subsequent steps, irrespect ive of the promoter, We conclude that the common role of CRP in the ac tivation of transcription is to stimulate events leading to the format ion of a productive open complex at a diverse set of CRP-dependent pro moters, We suggest that the interaction between CRP and RNAP is needed only transiently for the activation of transcription.