CLONING AND SEQUENCING OF RAT-KIDNEY L-ARGININE-GLYCINE AMIDINOTRANSFERASE - STUDIES ON THE MECHANISMS OF REGULATION BY GROWTH-HORMONE AND CREATINE

L-Arginine-glycine amidinotransferase (transamidinase) is the first an d rate-limiting step in creatine biosynthesis. Rats fed a creatine-sup plemented diet or hypophysectomized rats have only 20% of the kidney t ransamidinase activity as intact rats fed a creatine-free diet. A cDNA clone corresponding to transamidinase was isolated by immunoscreening of a lambda gt11 expression library prepared from rat kidney mRNA. Th e transamidinase cDNA had an open reading frame containing the known s equence of the amino terminal peptide of transamidinase. Based on the cDNA sequence, transamidinase is synthesized as a precursor with an am inoterminal extension of 50 amino acids, consistent with its mitochond rial localization. Comparison of the transamidinase sequence with the protein data base identified only a single, related protein. Remarkabl y, this protein, which has a 37% amino acid identity with transamidina se, is also an amidinotransferase, catalyzing streptomycin biosynthesi s in Streptomyces griseus. Transamidinase cDNA was used to investigate the regulation of mRNA levels by creatine and growth hormone. Hypophy sectomized rats were fed a creatine-free or a creatine-supplemented di et and maintained with and with out injections of growth hormone. An e xcellent correlation was found between changes in transamidinase activ ity and mRNA levels in response to creatine and growth hormone. Thus, the regulation of transamidinase by creatine and growth hormone is at a pretranslational level. In addition, the two effecters do not act in dependently but interact at a pretranslational level to control transa midinase gene expression.