A Tal1 cDNA cloned from a mouse erythroleukemic cell line was cloned downstream of the mouse Lck promoter. 3' splice and polyA sequences were derived from the human growth hormone gene. Transgene expression in the thymus was high after birth and continued at low levels throughout adulthood. Six lines were created (4709, 4719, 4722, 4723, 4726, and 4727) and line 4709 was selected as the representative line.