Copyright ©) 1994, American Society for Microbiology Nucleotide Sequence of the Streptococcus gordonii PK488

Human oral viridans group streptococci that coaggregate with Actinomyces naeslundii PK606 express surface proteins related to ScaA, the coaggregation-mediating adhesin of Streptococcus gordonii PK488 (R. N. Andersen, N. Ganeshkumar, and P. E. Kolenbrander, Infect. Immun. 61:981-987, 1993). The nucleotide sequence of the 6,125-bp EcoRI insert of pRA1, containing scaA, the gene encoding ScaA, was determined. Six open reading frames (ORFs) were identified. The orientation of four ORFs, two upstream (ORF 1 and ORF 2) and one downstream (ORF 4) ofscaA (ORF 3), indicated transcription in one direction, whereas ORF 5 and ORF 6 were transcribed divergently. Computer analysis of the deduced amino acid sequences identified a consensus binding site for ATP (GxxGxGKS) in the putative 28,054-Da protein encoded by ORF 1. ORF 2 potentially encoded a hydrophobic protein of 29,705 Da with six potential membrane-spanning regions. ScaA was 310 amino acids, 34,787 Da, and contained the lipoprotein consensus sequence LxxC, also reported for the ScaA-related proteins SsaB, FimA, and PsaA from Streptococcus sanguis 12, Streptococcus parasanguis FW213, and Streptococcus pneumoniae R36A, respectively. ORF 4 potentially encoded a 163-amino-acid protein of 17,912 Da, which was nearly identical to the downstream adjacent gene products of ssaB, fimA, and psaA. No significant homology with other proteins was found with the putative ORF 5 gene product, a 229-amino-acid protein of 25,107 Da. ORF 6 was incomplete and encoded a protein larger than 564 amino acids. This putativ