SMAR1, a novel, alternatively spliced gene product, binds the scaffold/matrix-associated region at the T cell receptor beta locus

Rearrangement and expression of the T cell receptor beta gene are critical events for early T lymphocyte development. To characterize cis-regulatory e lements and their associated trans-factors that mediate these events, we ha ve previously identified a nuclear matrix/scaffold-associated region, refer red to as MAR beta, 400 bp upstream of the E beta enhancer. Electrophoretic mobility shift assay showed that two known MAR-binding proteins, SATB1 and Cux, bind MAR beta, In this article, we report the identification of a nov el MAR-binding protein, named SMAR1, that also binds MAR beta. SMAR1 shares homology with SATB1 and Cux in the MAR-binding domain/Cut repeat and also with the tetramerization domain of a B cell-specific MAR-binding protein, B right. The binding of GST-SMAR1 fusion protein to MAR beta is inhibited by the presence of an excess amount of MAR-containing DNA from the immunoglobu lin kappa locus. Smar1 transcripts are most abundant in the thymus and are alternatively spliced. The smart gene maps to the distal portion of mouse c hromosome 8 at a distance of 111.8 cM. (C) 2000 Academic Press.