Identification of induced protein kinase activities specific for the ribosomal proteins uniquely phosphorylated during infection of HeLa cells with vaccinia virus

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Abstract
We have examined the ribosomal protein kinase activities in partially purified cytoplasmic extracts from HeLa cells infected with vaccinia virus. We found an activity or activities, absent from mock‐infected cells, that was capable of phosphorylating the proteins S2 and S13 in vitro. The ribosomes phosphorylated in vitro exhibited the same multiple phosphorylation of S2 found in vivo, at least 3 phosphoryl residues being seen, and the samemono‐phosphorylation of S13. Also as in vivo, ribosomal protein S2 contained phosphothreonine as well as phosphoserine, whereas S13 contained only phosphoserine. This strongly suggests that these new protein kinase activities are responsible for the ribosomal protein phosphorylations that occur during infection with vaccinia virus.