[Subunits of human holoenzyme of DNA dependent RNA polymerase III phosphorylated in vivo].

Phosphorylation of human holoenzyme of DNA dependent RNA polymerase III subunits in vivo has been investigated. RNA polymerase III from human placenta nuclei and epidermoid carcinoma cells A431 was isolated as two subfractions (IIIa and IIIb) distinguished in the order of elution from DEAE Sephadex A-25 column chromatography and buoyant density at glycerol gradient centrifugation. The subfractions of RNA polymerase III holoenzyme consists of four subunits with molecular masses 60, 52, 45 and 38 kDa, respectively, phosphorylated in vivo. The subunits with molecular masses 60 and 45 kDa are phosphorylated both on tyrosine and serine/threonine residues. All these subunits belong to subunits of the molecules of RNA polymerase III proper. RNA polymerase III and RNA polymerase I have the 38 kDa subunit in common. The subunit with molecular mass 52 kDa is phosphorylated on serine/threonine residues and may be related to some basal transcription factors of RNA polymerase III.