Comparative analysis of Xenopus tropicalis and Xenopus laevis vitellogenin gene sequences

Analysis of cDNA clones synthesized from vitellogenin mRNA of X. tropicalis revealed three different types of cDNA clones, i.e. A, A* and B. A and A* clones have a sequence divergence of about 6% and are both related to X. laevis vitellogenin cDNAs of subgroup A1 as well as A2 with a sequence divergence of 6-9%. B clones however, are related to X. laevis cDNA clones of subgroup B1 and B2 with a sequence divergence of about 7%. While the A and B clones correspond to vitellogenin mRNAs of similar abundance, A* clone is complementary to a vitellogenin mRNA about 100 fold less abundant than A and B mRNAs although all three vitellogenin mRNAs are encoded by single copy genes. Furthermore, two forms of A* mRNA were found. One of the two is lacking an internal fragment of about 900 bp. Since this DNA fragment is highly repeated in the genome, we suggest that this A* clone was synthesized from a processing intermediate of the A* precursor vitellogenin mRNA.