Excision products of the T cell receptor gene support a progressive rearrangement model of the alpha/delta locus.

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Abstract
We have cloned extrachromosomal circular DNAs containing T cell receptor (TCR) delta gene segments in adult mouse thymocytes and splenocytes. We find that the frequency of circular DNA clones carrying germline delta sequences is lower than that of J alpha probe‐positive clones, possibly related to increasing 5′ distance from the most upstream J alpha segment. This suggests that the TCR alpha/delta locus is successively rearranged from within and that the delta‐containing excision products are progressively diluted out by the subsequent cell division which includes further alpha gene rearrangements. In addition, examination of delta gene excision products revealed newly identified V delta subfamilies, the reciprocal joining of two D delta elements, J delta 2 usage in thymocytes and novel sequences homologous to the human delta‐gene deleting elements.