Upstream activating sequences that are shared by two divergently transcribed operons mediate cAMP-CRP regulation of pilus-adhesin in Escherichia coli.

Transcription of the genes encoding pilus-adhesin of serotype F13 in digalactoside-binding Escherichia coli required activation by the cAMP-CRP complex. Analysis of protein-DNA interaction in vitro showed that CRP bound in a cAMP-dependent manner to a sequence located 0.2 kb upstream of the point of transcription initiation of the pilus subunit operon. The cAMP-CRP activation included, in addition to the main pilus operon, the oppositely oriented operon encoding the Papl regulatory protein. Furthermore, the auto-regulatory product of the promoter-proximal gene (papB) in the pilus subunit operon was found to stimulate the papl transcriptional unit. Thus the cAMP-CRP complex and PapB might act in concert and indirectly promote pili synthesis by stimulating expression of the Papl positive regulator. The results of trans-complementation experiments and analyses using lacZ operon fusion derivatives showed that the cAMP-CRP activation also operated directly in cis on the pilus subunit operon. The region containing the CRP binding site appeared to function as an upstream activating sequence since deletion abolished expression even when the pap regulatory proteins Papl and PapB were supplied in trans. The implications for possible mechanisms of transcriptional activation by the cAMP-CRP complex at this novel location between the two oppositely oriented operons are discussed.