Promoter architecture of the Porphyromonas gingivalis fimbrillin gene

Porphyromonas gingivalis fimbriae can mediate adherence to many of the avai lable substrates in the oral cavity. Expression of P. gingivalis fimbriae i s regulated at the transcriptional level by environmental signals, such as temperature and hemin concentration. The arrangement of the upstream promot er and regulatory sequences required for transcription and control of the f imbrial structural gene fimA was investigated. Primer extension analysis de monstrated that the transcriptional start site of the fimA gene is located 41 bp upstream from the translational start codon. A region (upf) spanning 648 bp upstream of the start codon to 44 bp downstream of the translational start site was cloned upstream of a promoterless lacZ reporter gene. A ser ies of deletion and base substitution mutations were then generated in the upf region. The constructs were introduced into the chromosome of P. gingiv alis, and promoter activity measured by assaying levels of P-galactosidase. The results showed that fimA contains sequences resembling sigma(70) promo ter consensus sequences, consisting of a -10 region (TATGAC) located at -18 to -23 and a -35 region (TTGTTG) located at -41 to -46 from the transcript ional stare point. The AT-rich upstream sequences spanning bases -48 to -85 and bases -90 to -240 were required for full expression of the fimA gene, indicating the existence of positive regulation regions. Moreover, the -48 to -64 region may constitute an UP element, contributing to promoter activi ty in P. gingivalis. Thus, our data suggest that the P. gingivalis fimA gen e has a transcription complex consisting of -10 and -35 sequences, an UP el ement, and additional AT-rich upstream regulatory sequences.