CLONING, EXPRESSION AND MAP ASSIGNMENT OF CHICKEN PROSAPOSIN

Prosaposin is the precursor of four small glycoproteins, saposins A-D, that activate lysosomal sphingolipid hydrolysis. A fulllength cDNA en coding prosaposin from chicken brain was isolated by PCR. The deduced amino acid sequence predicted that, similarly to human and other mamma lian species studied, chicken prosaposin contains 518 residues, includ ing four domains that correspond to saposins A-D. There was 59 % ident ity and 76 % similarity of human and chicken prosaposin amino acid seq uences. The basic three-dimensional structures of these saposins is pr edicted to be similar on the basis of the conservation of six cysteine residues and an N-glycosylation site. Identity of amino acid sequence s was higher among saposins A, B and D than in saposin C. The predicte d amino acid sequence of saposin B matched exactly that of purified ch icken saposin B protein. The chicken prosaposin gene was mapped to a s ingle locus, PSAP, in chicken linkage group E11C10 and is closely link ed to the ACTA2 locus. This confirms the homology between chicken and human prosaposins and defines a new conserved segment with human chrom osome 10q21-q24.