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DNA‐activated protein kinase in Raji Burkitt's lymphoma cells: Phosphorylation of c‐Myc oncoprotein

IIJIMA, Shigeyuki, TERAOKA, Hirobumi, DATE, Takayasu, TSUKADA, Kinji
European journal of biochemistry 1992 v.206 no.2 pp. 595-603
RNA, lymphoma, oncogene proteins, phosphoproteins, phosphorylation, polyacrylamide gel electrophoresis, protein kinases, serine, single-stranded DNA
Autophosphorylation of a DNA‐activated protein kinase (DNA‐PK) in Raji Burkitt's lymphoma cells generated a band that corresponded to a phosphoprotein of about 300 kDa on SDS/PAGE. This band corresponds to a 300–350‐kDa DNA‐PK found previously in HeLa cells. In addition to the 300‐kDa phosphoprotein, the band of a highly phosphorylated 58‐kDa protein was detected by SDS/PAGE of partially purified DNA‐PK preparations after the phosphorylation reaction in the presence of double‐stranded DNA. this phosphoprotein was specifically immunoprecipitated by mAb against c‐Myc. More highly purfied preparations of DNA‐PK, containing neither a 58‐kDa phosphoprotein nor detectable activities of other kinases, phosphorylated recombinant c‐Myc proteins in the presence of DNA. the c‐Myc phosphorylation by DNA‐PK was markedly stimulated by relxed, double‐stranded DNA, but neither by single‐stranded DNA nor by RNA. Phosphopeptide mapping and phosphoamino acid analysis indicated that DNA‐PK phosphorylates c‐Myc in vitro at several serine residues.