Identification of a recombinational signal sequence-specific DNA-binding protein(s) of Mr 115,000 in the nuclear extracts from immature lymphoid cell lines.

Rearrangements of immunoglobulin genes are mediated by highly conserved heptamer and nonamer recombinational signal sequence. Using a protein-blotting procedure, a heptamer and nonamer recombinational signal sequence-specific DNA-binding protein(s) was examined in the nuclear extracts from lymphoid and nonlymphoid cell lines. Nuclear extracts were subjected to SDS-polyacrylamide gel electrophoresis, and transferred by electroblotting to nitrocellulose filters. Then the filters were hybridized to 32P-labelled synthetic double-stranded heptamer-23bp-nonamer or nonamer-12bp-heptamer recombinational signal sequence probes. A relatively large amount of a DNA-binding protein(s) of Mr 115,000 for both probes was detected in the nuclear extracts from immature B and immature T cell lines. No DNA-binding proteins were detected in a myeloma cell line. Interestingly, this DNA-binding protein(s) might be able to recognize both heptamer and nonamer. Recombinational signal sequence-specific DNA-binding activity of the protein(s) and the presence of the protein(s) in a stage-specific manner strongly suggest that the protein(s) of Mr 115,000 detected here may play an important role in the recombination of Ig and TCR genes.