POSTTRANSCRIPTIONAL REGULATION OF GLUTAMYL-PROLYL-TRANSFER-RNA SYNTHETASE IN RAT SALIVARY-GLAND

Treatment of rats with isoproterenol resulted in elevated levels of pr olyl- and glutamyl-tRNA synthetase activities in the parotid and subma ndibular glands. This increase in enzyme activity was accompanied by a n increase in the bi-functional glutamyl-prolyl-tRNA synthetase and of a low molecular weight form of prolyl-tRNA synthetase. Isoproterenol also induced the synthesis of proline-rich glycoproteins in the paroti d and submandibular glands. Withdrawal from the drug was accompanied b y a decline in prolyl- and glutamyl-tRNA synthetase activities and by a decline in the levels of proline-rich glycoproteins in the salivary gland. During the time course of isoproterenol treatment, little chang e in the levels of mRNA encoding the bi-functional glutamyl-prolyl-tRN A synthetase was detected by Northern blot analysis. These results ind icate that the synthesis of glutamyl-prolyl-tRNA synthetase is regulat ed at a posttranscriptional step and that the synthesis of this bifunc tional protein may be linked to the utilization of proline and glutami c acid in protein synthesis.