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

A genomic Eco RI DNA fragment of 4291 base pairs contains threeVβgenes, (V44T0,V44T1,andV44T2),each represented as only a single copy in the haploid genome of the rabbit. TheseVβdo not appear to be pseudogenes; all three can be found on ∼ 1.3 kb (mature size) transcripts in thymus RNA, although they do not contain classical upstream promoter sequences.VβT0andT1exhibit high DNA sequence homologies with mouseVβ10 andVβ1 genes, respectively ( ∼ 81 and 73 %). In the mouse, the two genes are also closely linked. RabbitVβgeneT2resembles mouseVβ11 and human YT35 DNA sequences but the homologies are lower (∼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 rabbitVβgenes are remarkably different from each other (∼ 54–65 %DNA; ∼ 33–55 %protein homologies). These facts suggest early duplication ofVβgenes and evolutionary conservation of certain members.