The transgene contains 1kb of genomic sequence 5' of the start codon and the entire coding sequence of the murine gene through exon 11. Exon 12 is derived from mouse cDNA sequence. These fragments are linked to a 3' untranslated region segment from hGH containing a single polyadenylation site. The resulting transgene is under the control of the proximal promoter element of the mouse gene and results in the production of 70 pg of mRNA per ug of total RNA.