24 human T cell receptor alpha chain messages have been examined by cDNA sequence analysis and Southern blot. The data indicate that there are approximately 40 alpha chain T cell receptor variable gene segments, which can be divided into 12 families. Comparison of the J gene segments from the cDNAs to previously determined germline J alpha sequences places the number of J alpha gene segments over 21, and indicates their number to be approximately 55. Identical nucleotide sequences in independent isolates of V alpha and J alpha gene segments indicate that hypermutation may not be a common mechanism for the expansion of diversity in these genes, and suggest that the major source of diversity within the alpha chain repertoire is a result of recombinational joinings between germline V alpha and J alpha sequences, combined with imprecise junctional joining. Analysis of the V regions of these alpha chain messages reveals the presence of three domains of hypervariability roughly analogous to the CDR1, CDR2, and CDR3 regions of immunoglobulin.

This content is only available as a PDF.