Mutational analysis of the promoter region of the porA gene of Neisseria meningitidis

The porA gene encodes the class 1 outer membrane protein (OMP1) in Neisseri a meningitidis and is under transcriptional control. Promoter regions of po rA from different clinical isolates were sequenced and were found to differ in the number of guanosine residues in a poly(G) track located upstream of the - 10 region. Isolates that did not express OMPI had up to nine G resid ues in the poly(G) track or an adenosine residue within this poly(G) track. Using beta-galactosidase as a reporter gene, the transcriptional activitie s of the promoter regions of the porA gene from three strains, two of which do not express OMP1, were assayed in both Escherichia coli and N. meningit idis. Mutations in the poly(G) track were created by site-directed mutagene sis and promoter fusions were further analyzed in E. coli and N, meningitid is. The number of nucleotides in the poly(G) track influenced promoter acti vity: reduction of a poly(G) track of 12 nt by one and by two guanosine res idues reduced promoter activity. Within the poly(G) track, replacement of a n adenosine residue by a guanosine residue increased the promoter activity; replacement of a guanosine residue by an adenosine residue decreased the a ctivity. The similar transcriptional activities for the mutated promoters i n E. coli and N. meningitidis are compatible with similar control mechanism s for transcriptional control in both organisms. (C) 1999 Elsevier Science B.V. All rights reserved.