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J A Traugh

Publications and source records attributed to J A Traugh.

At least 55 records · Page 3Linked to original sources
PubMed1992

Determinants on simian virus 40 large T antigen are important for recognition and phosphorylation by casein kinase I.

Casein kinase I has been shown to phosphorylate Ser123 and possibly Thr124, in simian virus 40 (SV40) large T antigen; the same sites are also modified in cultured cells incubated with 32Pi [Friedrich A. Grässer, Karl H. Scheidtmann, Polygena T. Tuazon, Jolinda A. Traugh & Gernot Walter (1988) Virology 165, 13-22]. The peptide, A-D-S-Q-H-S-T-P-P, which corresponds to the amino acid sequence 118-125 of SV40 large T antigen, was synthesized together with peptides containing changes in specific amino acid residues on either side of Ser123. These peptides were used as model substrates to determine the amino acids in the SV40 large T antigen important for recognition by casein kinase I. The native peptide identified above, with aspartate at the -4 position, was a poor substrate for casein kinase I in vitro. Peptides with acidic residues added at the -2 and -3 positions, preceding Ser123, were phosphorylated by casein kinase I with apparent Km values around 2 mM and Vmax values up to 500 pmol.min-1.ml-1. When acidic residues were added at both sides of the phosphorylatable serine, the peptide had a first-order rate constant over 20-fold higher than peptides with acidic amino acid residues at the N-terminus only; the apparent Km value was 0.65 mM with a Vmax of 2900 pmol.min-1.ml-1. The effects of modifying Ser120 to phosphoserine were examined by addition of a recognition sequence for the cAMP-dependent protein kinase prior to Ser120. Prior phosphorylation of the peptide at Ser120 lowered the apparent Km to 0.061 mM and increased the Vmax to 360 pmol.min-1.ml-1, a 50-fold decrease in Km for casein kinase I and a 6-fold increase in Vmax as compared to the non-phosphorylated peptide. This indicates that Ser120, which has been shown to be phosphorylated in vivo, provides an appropriate recognition determinant for casein kinase I.

Amino Acid Sequence↗
PubMed1991

Phosphorylation of elongation factor 1 (EF-1) and valyl-tRNA synthetase by protein kinase C and stimulation of EF-1 activity.

A high Mr complex isolated from rabbit reticulocytes contains valyl-tRNA synthetase and the four subunits of elongation factor 1 (EF-1). Previously, valyl-tRNA synthetase and the alpha, beta, and delta subunits of EF-1 were shown to be phosphorylated in reticulocytes in response to phorbol 12-myristate 13-acetate (PMA). Phosphorylation of the complex was accompanied by an increase in both valyl-tRNA synthetase and EF-1 activity (Venema, R. C., Peters, H. I., and Traugh, J. A. (1991) J. Biol. Chem., 266, 11993-11998). To investigate phosphorylation of the valyl-tRNA synthetase EF-1 complex in vitro by protein kinase C, the complex has been purified to apparent homogeneity from rabbit reticulocytes by gel filtration on Bio-Gel A-5m, affinity chromatography on tRNA-Sepharose, and fast protein liquid chromatography on Mono Q. Valyl-tRNA synthetase and the beta and delta subunits of EF-1 in the complex are highly phosphorylated by protein kinase C (0.5-0.9 mol of phosphate/mol of subunit), while EF-1 alpha is phosphorylated to a lesser extent (0.2 mol/mol). However, the isolated EF-1 alpha subunit is highly phosphorylated (2.0 mol/mol). Phosphopeptide mapping of EF-1 alpha shows that the same sites are modified by protein kinase C in vitro and in PMA-treated cells. Phosphorylation of the valyl-tRNA synthetase.EF-1 complex results in a 3-fold increase in activity of EF-1 as measured by poly(U)-directed polyphenylalanine synthesis; no effect of phosphorylation is detected with valyl-tRNA synthetase and isolated EF-1 alpha. Thus, phosphorylation and activation of EF-1 by protein kinase C, which has been shown to occur in vitro as well as in reticulocytes, may have a role in PMA stimulation of translational rates.

Amino Acyl-tRNA Synthetases↗
PubMed1991

Phosphorylation of valyl-tRNA synthetase and elongation factor 1 in response to phorbol esters is associated with stimulation of both activities.

Valyl-tRNA synthetase from mammalian cells is isolated in a high Mr complex with elongation factor 1 (EF-1). This complex, which represents all of the valyl-tRNA synthetase activity and a significant portion of the EF-1 activity in rabbit reticulocytes, contains five polypeptides identified as valyl-tRNA synthetase and the four subunits of EF-1. In this study, we have examined the potential for regulation of the complex by phosphorylation of these components. The valyl-tRNA synthetase.EF-1 complex has been purified by gel filtration and tRNA-Sepharose chromatography from 32P-labeled rabbit reticulocytes stimulated by phorbol 12-myristate 13-acetate (PMA) and compared to the complex purified from control cells. One- and two-dimensional polyacrylamide gel electrophoresis and autoradiography show that valyl-tRNA synthetase and the alpha, beta and delta subunits of EF-1 are phosphorylated in vivo. Phosphorylation of each of the four proteins is increased 2-4-fold in response to PMA. Phosphorylation of valyl-tRNA synthetase in response to PMA is reproducibly accompanied by a 1.7-fold increase in aminoacylation activity, whereas phosphorylation of EF-1 is associated with a 2.0-2.2-fold stimulation of activity, as measured by poly(U)-directed polyphenylalanine synthesis. These data suggest that stimulation of translational rates in response to PMA is mediated, at least in part, by phosphorylation of valyl-tRNA synthetase and EF-1.

Animals↗
PubMed1991

Phosphorylation of casein kinase II.

Casein kinase II from rabbit reticulocytes is a tetramer with an alpha,alpha' beta 2 or alpha 2 beta 2 structure; the alpha subunits contain the catalytic activity, and the beta subunits are regulatory in nature [Traugh, J.A., Lin, W. J., Takada-Axelrod, F., & Tuazon, P. T. (1990) Adv. Second Messenger Phosphoprotein Res. 24, 224-229]. When casein kinase II is isolated from rabbit reticulocytes by a rapid two-step purification of the enzyme, both the alpha and beta subunits are phosphorylated to a significant extent. In vitro, purified casein kinase II undergoes autophosphorylation on the beta subunit. In the presence of polylysine and polyarginine, phosphorylation of the beta subunits is inhibited, and the alpha subunits (alpha and alpha') become autophosphorylated. The effectiveness of polylysine coincides with the molecular weight. With basic proteins, including a number of histones and protamine, autophosphorylation of both subunits is observed. With histones, autophosphorylation of each subunit can be greater than that observed with the autophosphorylated enzyme alone or with a basic polypeptide. Thus, the potential exists for modulatory proteins to alter the autophosphorylation state of casein kinase II. Taken together, the data suggest that phosphorylation of the alpha subunit of casein kinase II in vivo may be due to an unidentified protein kinase or due to autophosphorylation. In the latter instance, casein kinase II could be transiently associated with specific intracellular compounds, such as basic proteins, with a resultant stimulation of autophosphorylation.

Animals↗
PubMed1991

Characterization of the catalytic subunit of casein kinase II expressed in Escherichia coli and regulation of activity.

The catalytic (alpha) subunit of casein kinase II from Drosophila, cloned and expressed in Escherichia coli (Saxena, A., Padmanabha, R., and Glover, C. V. C., (1987) Mol. Cell. Biol. 7, 3409-3417), has been purified and characterized, and the properties have been compared to those of the holoenzyme. The catalytic subunit exhibits protein kinase activity with casein as substrate and is autophosphorylated. The specific activity of the purified subunit is 6% of the activity of the holoenzyme from reticulocytes or from Drosophila. The alpha subunit is a monomer, eluting at Mr = 40,000 upon gel filtration in high salt, but as part of an aggregate in low salt. The alpha subunit has been purified to apparent homogeneity by sequential chromatography on DEAE-cellulose, Mono S, and Mono Q. A single band, Mr = 37,000, is detected by silver staining following polyacrylamide gel electrophoresis. The isolated alpha subunit displays apparent Km values for beta casein, ATP, and GTP similar to those of the holoenzyme. The activity of the alpha subunit is inhibited by heparin with an I50 of 0.1-0.3 micrograms/ml, a value similar to that observed for the holoenzyme; autophosphorylation is also inhibited by heparin. Polylysine has no stimulatory effect on the activity of the catalytic subunit, as measured with casein and by autophosphorylation, but stimulates both activities with the holoenzyme. When physiological substrates for casein kinase II are examined, glycogen synthase and eukaryotic initiation factor 3 (eIF-3) (p120) are phosphorylated by the alpha subunit at a rate equivalent to that of the holoenzyme, while phosphorylation of eIF-3 (p67) is reduced 9-fold and eIF-2 beta is not modified. From these data, it can be concluded that the alpha subunit of casein kinase II is sufficient for catalysis, is autophosphorylated, and can be directly inhibited by heparin, whereas the beta subunit mediates the effects of basic stimulatory compounds and is involved in recognition and/or binding to specific physiological substrates.

Animals↗
PubMed1991

Phosphorylation of eIF-4F by protein kinase C or multipotential S6 kinase stimulates protein synthesis at initiation.

Eukaryotic initiation factor (eIF) 4F, a multiprotein cap binding complex, has been shown to be phosphorylated in vivo in response to phorbol 12-myristate 13-acetate and insulin (Morley, S.J., and Traugh, J.A. (1990) J. Biol. Chem. 264, 2401-2404; Morley, S.J., and Traugh, J.A. (1990) J. Biol. Chem. 265, 10611-10616). The effect of phosphorylation on the activity of purified eIF-4F, utilizing both protein kinase C and a multifunctional S6 kinase, previously identified as protease activated kinase II, has been examined; these protein kinases modify eIF-4F p25 and p220 and eIF-4F p220, respectively. Studies with an eIF-4F-dependent protein synthesis system showed that phosphorylation of eIF-4F with either protein kinase resulted in a 3-5-fold stimulation of translation relative to the nonphosphorylated control. Chemical cross-linking of eIF-4F to cap-labeled mRNA, showed that phosphorylation increased the interaction of both the p25 and p220 subunits of eIF-4F with the 5' end of mRNA. This effect was manifested by a stimulation of initiation complex formation as measured by an increase in the association of labeled mRNA with 40 S ribosomal subunits in the translation system. Thus, phosphorylation of eIF-4F enhances binding to mRNA, resulting in a stimulation of protein synthesis at initiation.

Animals↗
PubMed1991

Protein kinase C phosphorylates glutamyl-tRNA synthetase in rabbit reticulocytes stimulated by tumor promoting phorbol esters.

A high Mr synthetase core complex isolated from higher eukaryotes contains aminoacyl-tRNA synthetases specific for arginine, aspartic acid, glutamic acid, glutamine, isoleucine, leucine, lysine, methionine, and proline. Previously, five of the synthetases were shown to be phosphorylated in reticulocytes, and the glutaminyl- and aspartyl-tRNA synthetases were shown to be selectively phosphorylated in response to 8-bromo cAMP (Pendergast, A. M., Venema, R. C., and Traugh, J. A. (1987) J. Biol. Chem. 262, 5939-5942). Exposure of reticulocytes to phorbol 12-myristate 13-acetate stimulates the selective phosphorylation of one synthetase in the complex, glutamyl-tRNA synthetase. Only the glutamyl-tRNA synthetase is modified to a significant extent when the purified complex is phosphorylated in vitro by protein kinase C; up to 0.7 mol of phosphate is incorporated per mol of synthetase. Two-dimensional phosphopeptide mapping shows a single tryptic phosphopeptide, which is identical for the enzyme modified in vitro by protein kinase C or in phorbol 12-myristate 13-acetate-stimulated cells. Phosphorylation in vivo is reproducibly accompanied by a 38 +/- 10% reduction in aminoacylation activity of partially purified glutamyl-tRNA synthetase assayed in vitro. Phosphorylation in vitro has no detectable effect on aminoacylation. This difference may be due to the absence of a required effector molecule which alters activity by interaction with the phosphorylated synthetase. Glutamyl-tRNA synthetase is one of a growing number of translational components, including initiation factors, which are coordinately modified by protein kinase C in response to phorbol 12-myristate 13-acetate.

Animals↗
PubMed1991

A ribosomal protein S6 kinase copurifies with phosphatase-1 activating factor.

A highly purified preparation of phosphatase-activating kinase (Fa) from rabbit skeletal muscle phosphorylated ribosomal protein S6. The two activities copurified on DEAE-Sephadex, CM-Sephadex, and phosphocellulose chromatography and upon further chromatography on Sephacryl S-300 and FPLC Mono-S and Mono-Q columns. On the latter column, two separate peaks of Fa activity were observed when it was developed in Tris buffer as opposed to beta-glycerophosphate. S6 kinase activity was obtained only with the Fa which adhered to the resin. The Mr of the Fa and S6 activities was determined to be 83,200 by gel permeation on a Sephacryl S-300 column. The Fa preparation phosphorylated serine residues on S6; two tryptic phosphopeptides, A and C, were identified by two-dimensional phosphopeptide analysis. The enzyme also showed good activity toward initiation factor eIF-4B. Based on specificity toward ribosomal proteins and initiation factors, the Fa and a mitogen-stimulated S6 kinase purified from insulin-stimulated 3T3-L1 cells were similar. These results suggest that a form of Fa and an insulin-stimulated S6 kinase may be related or closely associated.

Animals↗
PubMed1991

Modulation of the mitogenic activity of eukaryotic translation initiation factor-4E by protein kinase C.

Eukaryotic initiation factor-4E (eIF-4E) binds to the cap structure of eukaryotic mRNAs and is a component of the cap-binding protein complex eIF-4F. eIF-4E is present in cells in limiting concentrations and is phosphorylated both in vivo and in vitro by protein kinase C (PKC). Recently, eIF-4E has been implicated as an intracellular transducer of extracellular growth signals; microinjection of recombinant eIF-4E into quiescent NIH 3T3 cells induced DNA synthesis. In the present report, the mitogenic activity of eIF-4E was examined after coinjection with PKC. Recombinant eIF-4E was phosphorylated by PKC at the same amino acid that is phosphorylated in cultured cells and reticulocytes in response to phorbol ester. At limiting concentrations of eIF-4E, coinjection with PKC induced a fivefold increase in the mitogenic activity of eIF-4E. Injection of PKC alone or coinjection of eIF-4E with cAMP-dependent protein kinase (PKA) or the Raf protein had no effect. These results suggest that the mitogenic activity of eIF-4E is enhanced by PKC-specific phosphorylation and that phosphate addition is a rate-limiting step in eIF-4E activity.

Animals↗
PubMed1990

Comparison of phosphorylation of elongation factor 1 from different species by casein kinase II.

One subunit of EF-1 or EF-1 beta gamma from Artemia salina, wheat germ and rabbit reticulocytes is modified by casein kinase II. The subunit corresponds to the low Mr subunit of EF-1 (26,000-36,000) which functions along with a higher Mr subunit (46,000-48,000), to catalyze the exchange of GDP for GTP on EF-1 alpha. The factor from Artemia and wheat germ is phosphorylated directly on serine by casein kinase II whereas a modulatory compound is required for phosphorylation of EF-1 from reticulocytes. Polylysine increases the rate of phosphorylation of EF-1 from reticulocytes by 24-fold; both serine and threonine are modified. This suggests that polylysine may be substituting for a physiological regulatory compound which modulates phosphorylation in vivo.

Animals↗
PubMed1990

Differential stimulation of phosphorylation of initiation factors eIF-4F, eIF-4B, eIF-3, and ribosomal protein S6 by insulin and phorbol esters.

Exposure of quiescent, serum-starved 3T3-L1 cells to insulin promotes phosphorylation of initiation factors eIF-4F, eIF-4B, and eIF-3 p120, as well as ribosomal protein S6. Phosphorylation of both the p25 and p220 subunits of eIF-4F is stimulated typically by 2.5-5-fold, with a 2-4-fold increase in phosphorylation of eIF-4B and eIF-3 p120. Optimal stimulation is observed by 10(-9) M insulin. A similar pattern of stimulation is seen upon treatment of 3T3-L1 cells with 1 x 10(-6) M phorbol 12-myristate 13-acetate (PMA). Two-dimensional phosphopeptide mapping of p25, isolated from quiescent, insulin- or PMA-stimulated cells, results in a single tryptic phosphopeptide, indicating a single phosphorylation site identical to that obtained with protein kinase C. A more complex phosphopeptide map is observed with the p220 subunit. Following PMA-stimulation of 3T3-L1 cells, phosphopeptide mapping of p220 results in a pattern similar to that observed in vitro with Ca2+/phospholipid-dependent protein kinase (protein kinase C). Following insulin stimulation, mapping of p220 results in the appearance of novel peptides. Upon prolonged exposure to PMA, the cells are no longer responsive to this mitogen and no stimulation of phosphorylation of eIF-4F, eIF-4b, eIF-3 p120, or S6 via a protein kinase C-dependent mechanism is observed. Addition of insulin to these down-regulated cells leads to stimulation of phosphorylation of eIF-4F p220, ribosomal protein S6, and to a lesser extent, eIF-4B; little or no stimulation of phosphorylation of eIF-4F p25 and eIF-3 p120 is observed. Thus, eIF-4F p220, eIF-4B and ribosomal protein S6 are phosphorylated via PMA-dependent and insulin-dependent pathways, whereas phosphorylation of eIF-4F p25 and eIF-3 p120 is stimulated only upon activation of protein kinase C. Phosphopeptide maps of eIF-4F p220 and ribosomal protein S6 suggest that protease-activated kinase II is one of the protein kinases involved in the insulin-stimulated response in protein kinase C-depleted cells.

Animals↗
PubMed1990

Association of initiation factor eIF-4E in a cap binding protein complex (eIF-4F) is critical for and enhances phosphorylation by protein kinase C.

Phosphorylation by protein kinase C of the mRNA cap binding protein purified as part of a cap binding protein complex (eIF-4F) or as a single protein (eIF-4E), has been examined. Significant phosphorylation (up to 1 mol of phosphate/mol of p25 subunit) occurs only when the protein is part of the eIF-4F complex. With purified eIF-4E, using the same conditions, up to 0.1 mol of phosphate can be incorporated. Tryptic phosphopeptide maps show that the site phosphorylated in the Mr 25,000 subunit of eIF-4F (eIF-4F p25) is the same as that modified in purified eIF-4E. Kinetic measurements obtained from initial rates indicate that the Km values for eIF-4F and eIF-4E are similar, although the Vmax is 5-6 times higher for the complex. Dephosphorylation of eIF-4F p25, previously phosphorylated with protein kinase C, occurs in reticulocyte lysate with a half-life of 15-20 min, whereas little dephosphorylation is observed after 15 min with the purified phosphorylated eIF-4E. Phosphorylation of eIF-4F on the p220 and p25 subunits does not affect the stability of the complex as indicated by gel filtration on Sephacryl S-300. However, addition of non-phosphorylated eIF-4E to the phosphorylated complex results in the dissociation of the complex. These results suggest that interaction of p25 with other subunits in the complex greatly affects phosphorylation/dephosphorylation of p25. Since the rate of phosphorylation/dephosphorylation is significantly greater in the complex, regulation of the cap binding protein by phosphorylation appears to occur primarily on eIF-4F.

Animals↗
PubMed1989

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.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1989

Phorbol esters stimulate phosphorylation of eukaryotic initiation factors 3, 4B, and 4F.

Eukaryotic initiation factor (eIF) 4F, a multiprotein cap binding complex, was isolated by m7 GTP-Sepharose affinity chromatography from rabbit reticulocytes incubated with [32P]orthophosphate. Following treatment of reticulocytes with phorbol 12-myristate 13-acetate (PMA) for 30 min, stimulation of phosphorylation of both the p25 and p220 subunits was observed (2.5-5-fold). Two variants were observed for p25 in the absence and presence of PMA when analyzed by two-dimensional gel electrophoresis. Only the more acidic of these was phosphorylated, with the level of phosphorylation increased upon PMA treatment. One main variant was observed for p220; following PMA stimulation, in addition to increased labeling of this variant, two more acidic phosphorylated variants were observed. Low levels of eIF-3 and -4B were associated with purified eIF-4F, and PMA treatment stimulated phosphorylation of eIF-3 (p170) by 2-4-fold and eIF-4B by 1.5-2.5 fold. Two-dimensional phosphopeptide mapping of p25 phosphorylated in the absence or presence of PMA generated a single tryptic phosphopeptide, suggesting a single phosphorylation site. A more complex phosphopeptide map was observed with p220 subunit. The maps for both subunits contained the same phosphopeptides as those obtained when eIF-4F was phosphorylated in vitro by the Ca2+/phospholipid-dependent protein kinase, indicating this protein kinase directly modulated eIF-4F in response to PMA.

Animals↗
PubMed1989

Comparative analysis of phosphorylation of translational initiation and elongation factors by seven protein kinases.

Four initiation factors (eIF-2, -3, -4B, and -4F), previously shown to be phosphorylated in vivo, are each phosphorylated to a significant extent in vitro (greater than 0.3 mol of phosphate/mol of factor) by at least three different protein kinases. An S6 kinase from liver, an active form of protease-activated kinase II which modifies the same sites on S6 as those phosphorylated in vivo in response to mitogens, phosphorylates the beta subunit of eIF-2, eIF-3 (p120-p130), eIF-4B, and eIF-4F (p220). The Ca2+, phospholipid-dependent protein kinase phosphorylates eIF-2 beta, eIF-3 (p170, p120-p130), eIF-4B, and eIF-4F (p220, p25). The cAMP-dependent protein kinase significantly modifies eIF-4B and, to a lesser extent, eIF-3 (p130). Casein kinase I incorporates phosphate only into eIF-4B, but to a limited extent. Casein kinase II phosphorylates eIF-2 beta, eIF-3 (p170, p120), and eIF-4B, while protease-activated kinase I modifies eIF-3 (p170, p120-p130), eIF-4B, and eIF-4F (p220). The mitogen-stimulated S6 kinase from 3T3-L1 cells, activated in response to insulin, does not phosphorylate any of the initiation factors. There is no significant incorporation of phosphate into eIF-2 alpha or -gamma, eIF-4A, eIF-4C, eIF-4D, EF-1, or EF-2 by any of the protein kinases examined. Phosphopeptide mapping of tryptic digests of the phosphorylated subunits shows that the individual protein kinases modify different sites. The sites phosphorylated in vitro reflect those modified in vivo as shown with eIF-4F in concomitant studies with reticulocytes treated with tumor-promoting phorbol ester (Morley, S.J., and Traugh, J. A. J. Biol. Chem., in press). Thus, we have identified multipotential protein kinases which modify four initiation factors phosphorylated in vivo and have shown that phosphorylation of these translational components can be coordinately regulated.

Kinetics↗
PubMed1989

Phosphorylation of avian retrovirus matrix protein by Ca2+/phospholipid-dependent protein kinase.

The matrix protein from avian myeloblastosis virus and the Rous sarcoma virus, Prague C strain, is a phosphoprotein. A comparison of the amino acid sequences shows these phosphoproteins are very similar. The sites of phosphorylation of the matrix protein purified from virions are identified as serine residues 68 and 106. Treatment with purified rabbit skeletal-muscle protein phosphatase 1 or 2A, selectively releases phosphate from serine 68, while alkali treatment releases phosphate from both sites. When analyzed as a substrate for six different protein kinases, only the Ca2+/phospholipid-dependent protein kinase modifies the matrix protein. The serine residues phosphorylated in vivo are identical to those phosphorylated in vitro by this protein kinase. The role of these phosphorylation events in viral production is discussed.

Amino Acid Sequence↗