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- Title
Promoter strength influences phase variation of neisserial <em>opa</em> genes.
- Authors
Belland, Robert J.; Morrison, S. G.; Carlson, John H.; Hogan, Daniel M.
- Abstract
The <em>opa</em> multigene family of <em>Neisseria gonorrhoeae</em> encodes 11 related outer-membrane proteins which phase vary <em>in vitro</em> and <em>in vivo</em>. Illegitimate recombination within direct pentameric DNA repeats, encoding the signal-peptide region of pre-Opas, leads to switches in expression states. Despite the conserved nature of the variation mechanism, specific genes are expressed at high frequencies in the transition from Opa- to Opa+. The genes which are expressed at elevated frequencies differ from the rest of the family with respect to promoter structure, based on sequence comparisons between the <em>opa</em> genes of strain MS11mk. We have analysed transcription of the <em>opa</em> gene family of <em>N. gonorrhoeae</em> MS11mk, focussing on the different promoters found among the 11 genes to determine whether increased levels of expression are associated with increased phase-variation rates. Primer extension and Northern blotting was used to assess the levels of transcription of three representative <em>opa</em> genes (<em>opaA, B</em> and <em>C</em>) in 'on' and 'off' states. Full-length <em>opa</em> mRNA was detected primarily in strains expressing the homologous gene. Truncated <em>opa</em> mRNA was constitutively expressed from all <em>opa</em> genes regardless of their expression state. Quantitative comparisons in <em>N. gonorrhoeae</em> were complicated by the simultaneous expression of all 11 genes and the cross-reactivity of mRNA probes. Expression levels from the individual promoters were therefore assessed by creating transcriptional and translational <em>lacZ</em> fusions to each of the representative opa promoters which lacked the DNA repeats responsible for variation. The expression levels were compared to the phase-variation rates of translational <em>opa::phoA</em> fusions containing the same promoters in addition to the corresponding coding repeat regions. A strong correlation was found between expression levels from the different promoters and the variation rates at which 'on' variants appeared from an 'off' population (i.e. <em>opaA</em> > <em>opaB</em> > <em>opaC</em>). These results provide an explanation for the favoured expression of specific Opa proteins and indicate that expression of <em>opa</em> genes may be regulated at the level of transcription.
- Subjects
NEISSERIA gonorrhoeae; MEMBRANE proteins; GENES; PROMOTERS (Genetics); MESSENGER RNA
- Publication
Molecular Microbiology, 1997, Vol 23, Issue 1, p123
- ISSN
0950-382X
- Publication type
Article
- DOI
10.1046/j.1365-2958.1997.1971556.x