The objective of this project is to understand how prolyl-tRNA synthetase is regulated in mammals. The submandibular gland of most rodents undergoes a dramatic hypertrophy when the animal is treated with isoproterenol or tannins. In response to this treatment, the submandibular gland synthesizes large quantities of a class of proline-rich glycoproteins which appear to protect the animal from the toxic and carcinogenic effects of dietary tannins. These proteins are also produced at high levels by human salivary gland. The dramatic induction of these proteins is accompanied by an increase in the activity of prolyl-tRNA synthetase. This system should be an excellent model for understanding how prolyl-tRNA synthetase is controlled in differentiated tissues. We propose: (1) to examine the time course of induction of prolyl-tRNA synthetase in the submandibular gland during isoproterenol treatment to determine to what extent the increase in activity is the result of increased accumulation of the enzyme; (2) to purify prolyl-tRNA synthetase to obtain important structural information concerning the protein and to understand what the relationship is between a relatively low molecular weight form of the enzyme and a form which appears to exist associated with other aminoacyl-tRNA synthetases; (3) to isolate and sequence cDNA clones to deduce the primary structure of the protein and to obtain nucleic acid probes for the analysis of mRNA levels; (4) to examine the transcription of the gene for prolyl-tRNA synthetase in isolated nuclei to determine to what extent regulation is at the level of transcription; (5) to isolate genomic clones with the aim of identifying sequences that may be important in the regulation of the transcription and expression of the gene. These studies will be aimed at understanding how the protein synthetic apparatus of a cell is modified to accommodate differentiated functions that may protect the organism from toxic environmental agents.