FIG. 1.

(A) Schematic representation of the fhbp locus within the genome of wild-type N. meningitidis strain MC58 and mutant strains Δnmb1869 and Δfhbp. In the null mutants, an erythromycin cassette used to replace the respective genes by allelic exchange is orientated in the same direction (Δfhbp) or in the opposite direction (Δnmb1869). Hairpin structures indicate the position of predicted rho-independent terminators. The stem-loop downstream of the fhbp gene is comprised of a 12-nt perfect palindromic sequence including the GCCGTCTGAA DNA uptake sequence (DUS) separated by 13 nt of loop and followed by a stretch of four Ts. DUS are often found in the base-paired stem of transcription terminators (48). The putative rho-independent terminator in the nmb1869-fhbp intergenic region is comprised of a similar 12-nt imperfect palindromic sequence in which the second DUS sequence has two mismatches, separated by 4 nt and followed by a stretch of three Ts. The relative positions of the radioactively labeled probes used in the Northern blot analysis are indicated under each gene. The figure provides a diagrammatic representation of the long bicistronic transcriptional unit linking the nmb1869 and fhbp genes and of the two monocistronic transcripts independently transcribed from their own dedicated promoters. (B and C) Northern blot analysis. Total RNA prepared from MC58, Δfhbp, and Δnmb1869 cultures grown to mid-log phase was run on an 0.8% denaturing agarose gel, transferred to a nylon membrane, and probed with radioactively labeled PCR products equivalent to 187 bp of the fhbp gene (B) and 142 bp of the nmb1869 gene (C). The relative positions of the molecular weight RNA ladder are shown.