Full-length porcine growth hormone (PGH) cDNA clones were isolated from a porcine pituitary cDNA library. When the coding portion of the PGH gene was cloned into an E. coli expression vector downstream from the powerful trc promoter, high levels of mRNA, but no protein were detected. Mutation directed by an oligodeoxynucleotide primer altered 5'-non-coding sequences and raised the level of PGH produced from undetectable to 15% of the total cellular protein. Alteration of four codons infrequently used by E. coli in the 5'-end of the gene produced no further increases.
