Caenorhabditis elegans cyclin A- and B-type genes: a cyclin A multigene family, an ancestral cyclin B3 and differential germline expression.

We have cloned cDNAs for Caenorhabditis elegans cyclins A1, B and B3. While cyclins A1 and B are most closely related to either A- or B-type cyclins of other species, cyclin B3 is less related to these cyclins. However, this cyclin is most similar to the recently identified chicken cyclin B3. Our identification of a Caenorhabditis homolog demonstrates that cyclin B3 has been conserved in evolution. Cyclin A1 is a member of an A-type multigene family; however the cyclin A1 cDNA only recognizes a single band on northern blots. A single-sized RNA is also observed for the cyclin B3 cDNA. In contrast, three different transcripts are observed for the cyclin B cDNA. Based on our analyses using RNAs from germline-defective mutants and from populations enriched for males, one cyclin B transcript is specific to the paternal germline. The two other cyclin B transcripts, as well as the cyclin A1 and cyclin B3 transcripts, are most abundant in the maternal germline and are only present at low levels in other tissues. Moreover, the 3' untranslated regions of each Caenorhabditis cyclin cDNA possess several copies of potential translational control elements shown in Xenopus and Drosophila maternal cyclin mRNAs to function during oogenesis and early embryogenesis.