DUPLICATION OF THE MHC-LINKED XENOPUS COMPLEMENT FACTOR-B GENE

We have previously reported the molecular cloning of the mammalian maj or histocompatibility complex (MHC) class III gene, complement factor B (Bf) from Xenopus laevis, and linkage of the gene to the frog MHC. H ere, we estimated the copy number of the Xenopus Bf gene by genomic So uthern blotting analysis and demonstrated that Xenopus laevis has two copies of the Bf gene. Both genes co-segregated with the MHC-linked HS P70 genes among 19 offspring of an f/r x f/r cross, indicating a close linkage of the two Bf genes to the frog MHC. Both genes are transcrib ed and contain open reading frames. When compared with the previously determined cDNA sequence (Xenopus Bf A), the predicted amino acid sequ ence of the second cDNA species (Xenopus Bf B) shows 82% overall ident ity. Polymerase chain reaction analysis indicated that all of the part ially inbred frogs with the f, r, g, and j MHC haplotypes, as well as 12 outbred frogs tested have both Bf genes, suggesting that the duplic ated Bf genes are stable genetic traits in Xenopus laevis.