COMPARISON OF A VITELLOGENIN GENE BETWEEN 2 DISTANTLY BELATED RHABDITID NEMATODE SPECIES

Three vitellogenin genes from the free-living nematode Caenorhabditis elegans have previously been characterized at the molecular level. In order to study evolutionary relationships within this poorly understoo d taxon, we have cloned a vitellogenin gene, CEW1-vit-6 from a distant ly related species belonging to the same family as C. elegans. Screeni ng of a genomic library with a probe to total poly(A+) RNA yielded thr ee clones that hybridized more intensely than all others, and all thre e corresponded to a single gene homologous to C. elegans vit-6. Compar ison of CEW1-vit-6 with Ce-vit-6 reveals both strong similarities and surprising differences. Like Ce-vit-6 the gene is about 5 kb long and contains four unusually small introns (38-41 nt), but only one interru pts the gene at the same location as a Ce-vit-6 intron. The promoter r egion contains five matches to Vitellogenin Promoter Element 1 (VPE1) and no matches to VPE2, both previously shown to be required for vir g ene transcription in C. elegans. Codon usage is in general similar to that of the Ce-vir genes, but a few codon biases are quite different. Alignment of the CEW1-vit-6 protein with the Ce-vit-6 and Ce-vit-2 pro ducts suggests the existence of two domains which have evolved at diff erent rates. Sequence comparison shows that nematode vitellogenins are much more closely related to vertebrate than to insect vitellogenins.