A cluster of rabbit T-cell beta-chain variable region genes

Abstract

A genomic Eco RI DNA fragment of 4291 base pairs contains three V beta genes (V44T0, V44T1, and V44T2), each represented as only a single copy in the haploid genome of the rabbit. These V beta do not appear to be pseudogenes; all three can be found on approximately 1.3 kb (mature size) transcripts in thymus RNA, although they do not contain classical upstream promoter sequences. V beta T0 and T1 exhibit high DNA sequence homologies with mouse V beta 10 and V beta 1 genes, respectively (approximately 81 and 73%). In the mouse, the two genes are also closely linked. Rabbit V beta gene T2 resembles mouse V beta 11 and human YT35 DNA sequences but the homologies are lower (approximately 63%). The deduced protein sequences of the rabbit and mouse gene pairs are also conserved and ratios of replacement changes to silent base changes are low, suggesting that there has been selection for conservation of certain portions of the protein sequences. In contrast, the DNA and deduced protein sequences of the adjacent closely linked rabbit V beta genes are remarkably different from each other (approximately 54-65% DNA; approximately 33-55% protein homologies). These facts suggest early duplication of V beta genes and evolutionary conservation of certain members.