Partial purification of Drosophila Kc cell RNA polymerase III transcription components. Evidence for shared 5 S RNA and tRNA gene factors.

Class III transcription components were fractionated from Drosophila Kc cells. By the use of successive DEAE-Sephadex and CM-Sepharose column chromatographies, two fractions were identified to contain distinct positive transcription components. The reconstitution of these two fractions and RNA polymerase III was essential for faithful in vitro transcription of cloned Drosophila tRNA and 5 S RNA genes. Further chromatography of one of these fractions using phosphocellulose and DEAE-cellulose did not separate additional components required for reconstitution of transcription. These fractions may contain generalized class III transcription factors, as suggested by the cofractionation of required tRNA and 5 S RNA transcription components. We present further evidence that tRNA and 5 S RNA genes share at least one common transcription component other than RNA polymerase III by the use of stable transcription complex formation and competition experiments.