A zebrafish vitellogenin gene (vg3) encodes a novel vitellogenin without aphosvitin domain and may represent a primitive vertebrate vitellogenin gene

By analysis of zebrafish EST (expressed sequence tag) clones from an adult cDNA library, we have identified 44 clones, about 11% of the adult EST clon es, encoding vitellogenins. These vitellogenin EST clones have been derived from at least seven distinct vitellogenin genes. One of the largest vitell ogenin cDNA clones, vg3, and its 5' extended clone isolated by 5' RACE (rap id amplification of cDNA ends)-PCR, have been sequenced completely. The ded uced complete sequence includes a predicted mature vitellogenin of 1233 ami no acids and a truncated signal peptide of 18 amino acids. Interestingly, t he predicted vitellogenin has no polyserine phosvitin domain. The lack of t he phosvitin domain was confirmed by isolation and sequencing of the vg3 ge nomic region. Phylogenetic analysis indicates that the phosvitinless vitell ogenin is an intermediate between invertebrate vitellogenins and all known vertebrate vitellogenins, and thus may represent a primitive vertebrate vit ellogenin. Like other vitellogenins in vertebrates, the phosvitinless vitel logenin is also synthesized mainly in the liver and weakly in the intestine . (C) 2000 Elsevier Science B.V. All rights reserved.