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

Abstract

Rearrangement and expression of the T cell receptor β gene are critical events for early T lymphocyte development. To characterize cis-regulatory elements and their associated trans-factors that mediate these events, we have previously identified a nuclear matrix/scaffold-associated region, referred to as MARβ, 400 bp upstream of the Eβ enhancer. Electrophoretic mobility shift assay showed that two known MAR-binding proteins, SATB1 and Cux, bind MARβ. In this article, we report the identification of a novel MAR-binding protein, named SMAR1, that also binds MARβ. 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, Bright. The binding of GST-SMAR1 fusion protein to MARβ is inhibited by the presence of an excess amount of MAR-containing DNA from the immunoglobulin κ locus. Smar1 transcripts are most abundant in the thymus and are alternatively spliced. The smar1 gene maps to the distal portion of mouse chromosome 8 at a distance of 111.8 cM.