Purification, characterization, and molecular cloning of carp hyosophorin

Carp hyosophorin (HSP) is purified from oocytes. It is a highly glycosylated protein (10% protein and 90% carbohydrate) of high molecular weight (>100 kDa) and is localized in the cortical granules of oocytes. During cortical reaction carp HSP is exocytosed into the perivitelline space and is rapidly cleaved to the low-molecular-weight forms of 20 to 30 kDa. The major part of carp HSP cDNA is composed of tandem repeats, the repetitive domain. A repeat is 36 base pairs (bp) in length, which encodes 12 amino acid residues. The sequences of repeats vary within a given cDNA and among different cDNAs. The predominant sequences of repeats are DDGSGSNATTTQ. In addition, the length of the repetitive domain is highly variable among different genes and cDNAs, and ranges from 170 to 1,010 bp. Transcription of carp HSP is restricted in oocytes and starts very early during oogenesis. Carp HSP is highly species-specific. The RNA of goldfish ovary shows no positive signals when probed by carp HSP cDNA.