RECOMBINATION SEQUENCE-BINDING PROTEIN IN THYMOCYTES UNDERGOING T-CELL RECEPTOR GENE REARRANGEMENT

Rearrangement of T-cell antigen receptor and immunoglobulin genes occu rs in immature lymphoid cells by an unknown mechanism. To identify com ponents of the rearrangement machinery, we isolated a population of mu rine thymocytes enriched for rearranging pre-T cells. In the nuclear f raction of these cells, we detected a protein that specifically bound the recombination sequences that flank T-cell receptor and immunoglobu lin genes and are required for their rearrangement. This protein recog nized both heptamer and nonamer motifs of the recombination sequence, separated by either 12 or 23 bp. The protein complexed with the recomb ination sequence oligonucleotide had an apparent molecular mass of 30 kDa. The binding characteristics of the protein and its presence in re arranging thymocytes and cell lines suggest that it could serve as the recognition unit of a recombinase complex.