The transgenic construct contained two copies of the Emu enhancer from the immunoglobulin heavy chain (Igh) gene inserted ~450 bp upstream of the transcription initiation sites of the mouse Pim1 gene, into whose 3' untranslated region (3' UTR) was inserted the LTR of the murine leukemia virus (MuLV). Line 64a carries an estimated 2-4 copies of the transgene. Northern blot analysis detects high levels of transgene-derived mRNA in kidney, as well as in thymus, spleen and bone marrow, but not in testis, of transgenic mice. Immunoblot analysis showed both proteins normally expressed from the endogenous Pim1 gene to be overexpressed in the trangenic thymus. Following antigen stimulation, splenic T and B lymphocytes both express high levels of transgenic mRNA.