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 modified so that phenylalanine is coded for at position 505 rather than tyrosine. 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 6 pg of mRNA per ug of total RNA.