A NEW MEMBER OF THE S-LAYER PROTEIN FAMILY - CHARACTERIZATION OF THE CRS GENE FROM CAMPYLOBACTER-RECTUS

Strains of the periodontal pathogen Campylobacter rectus express a 150 - to 166-kDa protein on their cell surface. This protein forms a parac rystalline lattice, called the surface layer (S-layer), on the outer m embrane of this gram-negative bacterium. To initiate a genetic analysi s of the function of the S-layer in the pathogenesis of C. rectus, we have cloned and characterized its gene. The S-layer gene (cps) from C. rectus 314 encodes a cell surface protein which does not have a cleav ed signal peptide at its amino terminus. Although the amino acid seque nce deduced from the crs gene has 50% identity with the amino-terminal 30 amino acids of the four S-layer proteins from Campylobacter fetus, the similarity decreases to less than 16% over the rest of the protei n. Thus, the crs gene from C. rectus encodes a novel S-layer protein w hose precise role in pathogenesis may differ from that of S-layer prot eins from other organisms. Southern and Northern blot analyses with pr obes from different segments of the crs gene indicate that the S-layer gene is a single-copy, monocistronic gene in C. rectus. RNA end mappi ng and sequence analyses were used to define the crs promoter; there i s an exact match to the Escherichia coli -10 promoter consensus sequen ce but only a weak match to the -35 consensus element. Southern blots of DNA from another strain of C. rectus, ATCC 33238, demonstrated that the crs gene is also present in that strain but that there are numero us restriction fragment length polymorphisms in the second half of the gene. This finding suggests that the carboxy halves of the S-layer pr oteins from strains 314 and 33238 differ. It remains to be determined whether the diversities in sequence are reflected in functional or ant igenic differences important for the pathogenesis of different C. rect us isolates.