Identification and characterization of serine/threonine protein kinase activity intrinsic to the L protein of vesicular stomatitis virus New Jersey

1 School of Biological Sciences and 2 Department of Biochemistry, Lucille P. Markey Cancer Center, University of Kentucky, Lexington, Kentucky 40506-0225, U.S.A. A photoaffinity analogue of ATP, 8-azido-adenosine 5'-triphosphate (8-N 3 ATP), was used to probe ATP-binding sites in native transcription complexes of vesicular stomatitis virus (VSV) (New Jersey serotype). The analogue was found to be a substrate for a serine/threonine protein kinase that phosphorylated both the NS and L proteins of native complexes. The analogue failed to interact with the RNA polymerase, another ATP-utilizing activity associated with the transcription complex. Kinetic analyses of both ATP and 8-N 3 ATP utilization by the protein kinase yielded biphasic saturation curves. Photolysis of 8-N 3 ATP in the presence of VSV transcription complexes resulted in selective labelling of the L protein. The photolabelling of L was saturable and apparently biphasic. Photolabelling of the L protein was significantly reduced by competition with ATP whereas other nucleoside triphosphates (GTP, UTP and CTP) were ineffective competitors. The stoichiometry of photolabelling was 0.2 at 10 µ M -8N 3 ATP and 1.3 at 100 µ M -ATP. These data provide chemical evidence for a virus-encoded serine/threonine protein kinase which resides on the L protein. Received 10 May 1991; accepted 30 September 1991.