IDENTIFICATION OF A T-CELL LINEAGE-SPECIFIC RNA DNA HELICASE AND ITS CELL-SURFACE EXPRESSION DURING INTRATHYMIC EDUCATION OF ALPHA-BETA ANDGAMMA-DELTA T-CELLS/

Despite ubiquitous expression of the gene, RNA/DNA helicase protein wa s found to be expressed specifically in all cells of the T cell lineag e. Interestingly, immature thymocytes that are rearranging T cell rece ptor (TCR) genes express the helicase strongly on the cell surface and the surface expression is terminated upon engagement of functional TC R by positively selecting ligands. This provides the first evidence th at a protein that binds nucleic acids can directly contact the extrace llular environment in a developmentally controlled manner. Our discove ry of a novel molecular link between the cell surface and nuclear even ts specific for thymocytes suggests that thymic education is supervise d by a previously unknown molecular mechanism, which can now be experi mentally explored.