Sequence analysis of the omp2 region of Chlamydia psittaci strain GPIC: structural and functional implications.

The nucleotide sequence of a 3.1-kb genomic DNA fragment carrying the omp3, omp2 and srp gene homologs from Chlamydia psittaci strain GPIC was determined. A comparative analysis of the GPIC sequence with other chlamydial omp2-linked sequences reveals highly conserved omp3 and omp2 upstream sequences across species, suggesting a unified mechanism of transcription regulation. In contrast, the omp2-srp intergenic segment, which encompasses hypothetical srp transcriptional initiation sites, is relatively less conserved in length and in sequence. Examination of the predicted translation products reveals a high degree of homology within Omp3 and Omp2 across species, with the notable exception of the N-terminal fifth of Omp2. Although the latter segment displays relatively high interspecies sequence variation, it includes a smaller segment, whose high positive charge density is conserved across species, suggesting a conserved structure/function. In contrast to Omp2 and Omp3, a comparative analysis of the predicted amino acid (aa) sequence of the srp product reveals high homology within species, but relatively little across species. A 38-aa segment near the C-terminus of Srp, whose sequence is 64% identical between C. psittaci GPIC and C. trachomatis, is partially truncated in C. psittaci 6BC.