A new locus (vsp417-4) belonging to the tsa417-like subfamily of variant-specific surface protein genes in Giardia intestinalis

A new variant-specific surface protein gene locus (vsp417-4) of Giardia int estinalis is described. Vsp417-4 represents the fourth member of a gene sub family that is based on a previously described gene, tsa417(= vsp417-1). Th e new locus was detected by characterising DNA amplified in polymerase chai n reactions from the 3' ends of divergent homologues (vsp417-4(A-I), vsp417 -4(A-II)) found respectively in isolates belonging to the genetic Assemblag e A/Group I ('A-I') and Assemblage A/Group II ('A-II') subtypes of G. intes tinalis. The complete vsp417-4(A-I) gene was isolated on a 6.2-kb HindIII f ragment by screening a genomic DNA library prepared from a type A-I isolate , Ad-1/C7. The deduced polypeptide (VSP417-4(A-I); 709 amino acids, Mr 7266 2) has properties characterising it as a Giardia variant-specific surface p rotein, namely a high cysteine content (11.85 mol%), 29 copies of the four amino-acid 'CXXC' motif, and conserved N-terminal signal peptide and C-term inal hydrophobic (membrane-spanning) segments-the latter terminating with t he invariant, hydrophilic motif '-CRGKA'. An extended polyadenylation signa l sequence (CTTAGRTAGTAAAY), which appears to be a characteristic feature o f VSP genes in Giardia, is situated immediately beyond the stop codon. VSP4 17-4(A-I) shares 87% sequence identity with VSP417-4(A-II) over its C-termi nal 235 amino acids, but only 57-58% identity with VSP417-1, VSP417-2 and V SP417-3 which are encoded by other vsp417 family genes identified in these genotypes. Southern hybridisations, using probes derived from the 5' segmen t of vsp417-4(A-I), indicated the presence of at least five to six closely related loci in both type A-I and type A-II isolates. (C) 1999 Elsevier Sci ence B.V. All rights reserved.