Phosphorylation of threonyl- and seryl-tRNA synthetase by cAMP-dependent protein kinase. A possible role in the regulation of P1, P4-bis(5'-adenosyl)-tetraphosphate (Ap4A) synthesis.
Threonyl-tRNA synthetase has been shown to be phosphorylated in reticulocytes (Dang, C. V., Tan, E. M., and Traugh, J. A., (1988) FASEB J. 2, 2376-2379). Upon incubation of reticulocytes with 8-bromo-cAMP, phosphorylation of threonyl-tRNA synthetase is stimulated approximately 2-fold, an increase similar to that observed with ribosomal protein S6. To analyze the effects of phosphorylation on activity, threonyl-tRNA synthetase has been purified to apparent homogeneity from rabbit reticulocytes utilizing a four-step purification procedure with the simultaneous purification of seryl-tRNA synthetase. Both synthetases are phosphorylated in vitro by the cAMP-dependent protein kinase. Prior to phosphorylation, the two synthetases produce significant amounts of P1, P4-bis(5'-adenosyl)-tetraphosphate (Ap4A) in the presence of the cognate amino acid and ATP, with activities comparable to that of lysyl-tRNA synthetase. Phosphorylation has no effect on aminoacylation, but an increase in Ap4A synthesis of up to 6-fold is observed with threonyl-tRNA synthetase and 2-fold with seryl-tRNA synthetase. Thus, cAMP-mediated phosphorylation of specific aminoacyl-tRNA synthetases appears to be a potential mode of regulation of Ap4A synthesis in mammals.
Dang
C V
CV
Department of Biochemistry, University of California, Riverside 92521.
Traugh
J A
JA
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000596:Amino Acids / Q000378:metabolism; D000604:Amino Acyl-tRNA Synthetases / Q000097:blood*; D000818:Animals; D002850:Chromatography, Gel; D015226:Dinucleoside Phosphates / Q000096:biosynthesis / Q000097:blood*; D006706:Homeostasis; D010766:Phosphorylation; D011494:Protein Kinases / Q000097:blood*; D011817:Rabbits; D012156:Reticulocytes / Q000201:enzymology*; D012714:Serine-tRNA Ligase / Q000097:blood* / Q000302:isolation & purification; D013914:Threonine-tRNA Ligase / Q000097:blood* / Q000302:isolation & purification
D000596:Amino Acids; D015226:Dinucleoside Phosphates; D015124:8-Bromo Cyclic Adenosine Monophosphate; C020733:diadenosine tetraphosphate; D011494:Protein Kinases; D000604:Amino Acyl-tRNA Synthetases; D012714:Serine-tRNA Ligase; D013914:Threonine-tRNA Ligase