ISOLATION AND CHARACTERIZATION OF GOLDFISH Y-BOX PROTEIN, A GERM-CELL-SPECIFIC RNA-BINDING PROTEIN

Cyclin B is a regulatory subunit of maturation-promoting factor. In go ldfish (Carassius auratus) oocytes, cyclin B is synthesized de novo af ter stimulation by 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (maturat ion-inducing hormone). In this study, we examined goldfish oocyte prot eins bound to cyclin B mRNA. Using oligo(dT)-cellulose affinity chroma tography and northwestern blotting analysis, we identified a 54-kDa cy clin B mRNA-binding protein (p54). Southwestern blotting analysis show ed the binding of p54 to the Y box DNA element (CTGATTGGCCAA), suggest ing that p54 is a Y box protein in goldfish. We isolated two cDNA clon es, GFYP1 and GFYP2, the latter of which encodes a germ-cell-specific Y box protein. An antibody against a GFYP2 protein recognized p54, sug gesting that p54 is identical or highly similar to GFYP2 protein. This is also supported by the finding that a recombinant GFYP2 expressed i n bacteria bound to both the Y box DNA element and the goldfish cyclin B mRNA synthesized ill vitro. These results suggest that p54 is a ger m-cell-specific Y box protein and is a potential masking protein of cy clin B mRNA in goldfish oocytes.