Potential regulatory elements of nematode vitellogenin genes revealed by interspecies sequence comparison.

The nematode, Caenorhabditis elegans, has a six-member gene family encoding vitellogenins, the yolk protein precursors. These genes are expressed exclusively in the intestine of the adult hermaphrodite. Here we report the cloning of all five members of the homologous gene family from another Caenorhabditis species, Caenorhabditis briggsae. Nucleotide sequence analysis of these genes reveals they are about 85% identical to the C. elegans genes in the coding regions. Overall similarity is much reduced in noncoding and flanking regions. However, two repeated heptamers, previously identified in the upstream regions of the C. elegans genes, are largely conserved in both location and sequence in C. briggsae. Conservation of certain of these heptamers suggests that proteins bound at these positions may be especially important to promoter function and/or regulation. Comparative sequence analysis also suggests the possibility that the first 70 bases of the vitellogenin mRNAs can be folded into stable secondary structures. Almost all base differences between the two species occur in sequences predicted to be unpaired, suggesting that the ability to form intrastrand base pairs has been selected during Caenorhabditis evolution.