Comparative Biochemistry and Physiology Part B 135 (2003) 71–81 1096-4959/03/$ - see front matter  2003 Elsevier Science Inc. All rights reserved. doi:10.1016/S1096-4959(03)00084-8 Cleavage site of a major yolk protein (MYP) determined by cDNA isolation and amino acid sequencing in sea urchin, Hemicentrotus pulcherrimus Yukio Yokota *, Tatsuya Unuma , Akihiko Moriyama , Keisuke Yamano a, b c b Department of Applied Information Technology, Aichi Prefectural University, Nagakute, Aichi 480-1198, Japan a National Research Institute of Aquaculture, Nansei, Mie 516-0193, Japan b Graduate School of Natural Sciences, Nagoya City University, Mizuho, Nagoya 468-8501, Japan c Received 14 November 2002; received in revised form 4 March 2003; accepted 5 March 2003 Abstract The overall sequence of cDNA encoding vitellogenin (Vg), a precursor to major yolk protein (MYP),of Hemicentrotus pulcherrimus was determined. Its nucleotide sequence has an open reading frame of 4041 bp encoding 1346 amino acids. The amino acid sequence showed little similarity to other Vgs in vertebrates, insects or nematodes, but resembled members of the vertebrate and invertebrate transferrin family. The N-terminal amino acid sequence of the protein fragments dominant in the later embryonic stage was analyzed in order to determine the cleavage site of MYP. Determination of the cleavage site in MYP and analysis of MYP proteolysis in vitro suggested that MYP has a specific molecular shape to permit its proteolytic fragmentation at a definite site. The functional region of transferrin in MYP is conserved after proteolytic processing. Considering these results and those from other work, the protein called sea urchin Vg is not a true Vg. Therefore, a new name, echinoferrin, is proposed for this protein.  2003 Elsevier Science Inc. All rights reserved. Keywords: Sea urchin; Hemicentrotus pulcherrimus; Yolk protein; Ovary; Development; Proteolysis; Transferrin; Egg; Embryo; Echinoferrin 1. Introduction Precursors to the yolk proteins of oviparous animals are divided into two groups. One contains relatively smaller yolk proteins of approximately 45 kDa, which are mostly found in dipterans. The other is a larger protein with a molecular weight of approximately 170–220 kDa called Vg, which occurs in various phyla, nematodes, echinoderms, vertebrates, crustaceans and insects other than *Corresponding author. Tel.: q81-561-64-1111; fax: q81- 561-64-1108. E-mail address: yokota@ist.aichi-pu.ac.jp (Y. Yokota). dipterans. The proteins called Vg have various characteristics and differ among taxa. The precursor to major yolk protein (MYP) of the sea urchin shows different characteristics from Vg of vertebrates, insects and molluscs. The char- acteristic specific to sea urchin Vg is that it is not a female-specific protein. Its occurrence in the coelomic fluid of both sexes at the same concen- tration throughout the year raised an intriguing question on the biological function of Vg inde- pendent of sex (Harrington and Easton, 1982; Shyu et al., 1986; Unuma et al., 1998). Vg was reported to be synthesized in directly developing