title: A new locus (vsp417-4) belonging to the tsa417-like subfamily of variant-specific surface protein genes in Giardia intestinalis.
abstract: A new variant-specific surface protein gene locus (vsp417-4) of Giardia intestinalis is described. Vsp417-4 represents the fourth member of a gene subfamily that is based on a previously described gene, tsa417 ( =vsp417-1). The new locus was detected by characterising DNA amplified in polymerase chain reactions from the 3' ends of divergent homologues (vsp417-4(A-I), vsp417-4(A-II)) found respectively in isolates belonging to the genetic Assemblage A/Group I ('A-I') and Assemblage A/Group II ('A-II') subtypes of G. intestinalis. The complete vsp417-4(A-I) gene was isolated on a 6.2-kb HindIII fragment 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 72662) has properties characterising it as a Giardia variant-specific surface protein, 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-terminal hydrophobic (membrane-spanning) segments--the latter terminating with the invariant, hydrophilic motif '-CRGKA'. An extended polyadenylation signal sequence (CTTAGRTAGTAAAY), which appears to be a characteristic feature of VSP genes in Giardia, is situated immediately beyond the stop codon. VSP417-4(A-I) shares 87% sequence identity with VSP417-4(A-II) over its C-terminal 235 amino acids, but only 57-58% identity with VSP417-1, VSP417-2 and VSP417-3 which are encoded by other vsp417 family genes identified in these genotypes. Southern hybridisations, using probes derived from the 5' segment 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.
authors.affiliation: Department of Microbiology and Immunology, The University of Adelaide, SA, Australia. pey@microb.adelaide.edu.au
authors.forename: P L
authors.initials: PL
authors.lastname: Ey
authors.forename: J M
authors.initials: JM
authors.lastname: Darby
authors.forename: G
authors.initials: G
authors.lastname: Mayrhofer
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D000953:Antigens, Protozoan / Q000737:chemistry / Q000235:genetics*; D000954:Antigens, Surface / Q000737:chemistry / Q000235:genetics*; D015139:Blotting, Southern; D019143:Evolution, Molecular; D017125:Genes, Protozoan; D016829:Giardia lamblia / Q000145:classification / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D016133:Polymerase Chain Reaction / Q000379:methods; D015800:Protozoan Proteins; D015183:Restriction Mapping; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D000953:Antigens, Protozoan; D000954:Antigens, Surface; D015800:Protozoan Proteins; C072464:variant surface protein H7, Giardia lamblia