THE STAPHYLOCOCCUS-AUREUS COLLAGEN ADHESIN-ENCODING GENE (CNA) IS WITHIN A DISCRETE GENETIC ELEMENT

Although the gene (cna) encoding the Staphylococcus aureus (Sa) collag en adhesin is not present in all strains, the DNA both upstream and do wnstream of nra is present in all Sa strains. Using oligo primers corr esponding to the conserved nt flanking cna and template DNA from Sa st rains that do not encode cna, we amplified a 372-bp fragment. These re sults illustrate that the conserved regions upstream and downstream of cna are contiguous in strains that do not encode cna. Using primers c orresponding to the conserved flanking DNA together with primers corre sponding to the 5' and 3' ends of cna, we also amplified DNA fragments containing the junctions between the cna genetic element and the cons erved flanking sequences. Sequence comparisons of the amplification pr oducts from four cna negative and four cna positive strains revealed t hat cna is within a discrete genetic element that extends 202 bp upstr eam from the cna start codon and 100 bp downstream of the cna stop cod on. Sequence analysis of the ends of the cna element did not reveal an y of the repeats characteristic of transposable elements. These result s suggest that cna may be part of a larger element (e.g., a phage) tha t may or may not contain cna. Alternatively, cna may be a subject to a precise excision event resulting in its deletion from the chromosome. Based on sequence analysis of the flanking DNA amplified from strains that do not encode cna, the presence of a cna genetic element does no t disrupt an ORF. (C) 1997 Elsevier Science B.V.