Purification and characterization of a nucleoplasmin-like protein from carp (Cyprinus carpio) eggs

Nucleoplasmin, first isolated from Xenopus laevis eggs, promotes nucleosome assembly. Hereby, we have purified a nucleoplasmin-like protein from carp (Cyprinus carpio) eggs using ion exchange and subsequent gel filtration columns. The protein was recognized by a polyclonal antiserum against Xenopus laevis nucleoplasmin and had an amino acid composition similar to other member of the nucleoplasmin family proteins. Partial amino acid sequences from the cyanogen bromide (CNBr)-cleaved fragments showed high homology with Xenopus nucleoplasmin. The protein was also found to form an oligomeric complex and to be phosphorylated. Moreover, this protein promoted sperm nuclear decondensation as well as that of nucleoplasmin from Xenopus laevis eggs. These results suggest that the fish protein isolated here is a member of nucleoplasmin family.