A conserved sequence block in the murine and human T cell receptor Jalpha loci interacts with developmentally regulated nucleoprotein complexes in vitro and associates with GATA-3 and octamer-binding factors in vivo.

A highly conserved sequence block (CSB) located in the mouse and human T cell receptor (TCR) Jalpha loci is recognized by tissue-specific factors and up-regulates TCR alpha enhancer activity. In this study, the properties of CSB-interacting factors were further explored to decipher the function of this cis-acting element. Thymocytes corresponding to different developmental stages were found capable of forming differential CSB-nucleoprotein complexes. Pronounced changes in the CSB-complex-forming activity were observed during the transition from double-negative to double-positive thymocytes. Furthermore, we showed that transcription factors Oct-1, Oct-2 and GATA-3 interacted with CSB both in vitro, as evidenced by electrophoretic mobility shift assays, and in vivo, as demonstrated by chromatin immunoprecipitation assays in mouse thymus. Importantly, we also demonstrated that GATA-3 associated in vivo with TCR alpha enhancer, the activity of which is known to be required in regulating chromatin accessibility to the V(D)J recombinase. Thus, CSB may temporally regulate local chromatin structure and help to spread TCR alpha enhancer activity over the entire 70-kb Jalpha locus by forming developmentally regulated CSB-nucleoprotein complexes and by interacting with other cis-regulatory element-nucleoprotein complexes present within the TCR alpha / delta locus.