Analysis of transcriptional control mechanisms of capsule expression in Neisseria meningitidis.

The major virulence factor which contributes to the survival of Neisseria meningitidis in the blood stream and the cerebrospinal fluid is the capsular polysaccharide. Expression of the capsule genes of N. meningitidis serogroups B, C, W-135 and Y is controlled by an intergenic region separating the capsule biosynthesis operon (siaA-D) and the capsule transport operon (ctrA-D). To further investigate capsule expression in N. meningitidis we amplified and sequenced the intergenic region of 42 meningococcal isolates of different serogroups. Sequence variations were found mainly in a repeat region preceding the siaA start codon. Correlation between sequence variation and serogroup could not be observed. To measure the transcriptional and translational activity of the respective intergenic regions we performed transcriptional and translational fusions with the lacZ gene integrated into the chromosome of N. meningitidis. Sequence variations preceding the siaA start codon had no effect on beta-galactosidase activity. Different in vitro growth conditions such as temperature, glucose concentration, osmolarity, pH and iron concentration also did not influence beta-galactosidase activity. Sequential deletions of the intergenic region showed that an Up-like element adjacent to the predicted -35 box is necessary for full transcriptional activity. The deletion of the untranslated region preceding the siaA start codon led to a threefold higher beta-galactosidase activity compared with the full-length construct suggesting that the respective region may be involved in capsule regulation.