AN IS4 INSERTION AT THE GLNA CONTROL REGION OF ESCHERICHIA-COLI CREATES A NEW PROMOTER BY PROVIDING THE -35 REGION OF ITS 3'-END

An insertion element (IS)4 insertion selected as suppressor of the rpo N73::Tn5 alelle was located inside the control region of the glnA gene in Escherichia coli. In the rpoN73::Tn5 background the IS4 insertion promotes glnA transcription at a low constitutive level sufficient to sustain glutamine-independent growth. The IS4 insertion mutation in ei ther rpoN73::Tn5 or wild-type backgrounds promotes glnA transcription from a new start site located mio bases downstream of the glnAp2 start site. Analysis of sequences flanking the insertion point showed a pro moter sequence whose -35 region was located inside the IS4 sequence an d the -10 region was inside the glnA control region. Site-directed mut agenesis of relevant nucleotide residues of the newly created promoter impaired transcription of a reporter gene. The results support our co ntention that IS4 carries a -35 promoter region that is able to create functional hybrid promoters. We propose that this mechanism could be one of the molecular reasons of the suppressor activity previously rep orted for IS4. (C) 1998 Academic Press.