Ribonucleic Acid Polymerase from Eukaryotic Cells

The role of protein factor B and C on RNA synthesis by RNA polymerase CI isolated from chromosomal non‐histone proteins of coconut nuclei has been studied further. Factor B has been implicated as the initiation factor on the experimental evidences that (a) in its absence, RNA polymerase CI shows only minimal activity; (b) it can bind with RNA polymerase and the enzyme · factor B complex then binds to DNA, but factor B alone can not bind to DNA; (c) it promotes the incorporation of [β,γ‐ 32 P 2 ]ATP into RNA and this stimulation reaches a plateau rather quickly while the incorporation of [ 14 C]ATP in the interior of RNA chain continues; (d) it is active with native homologous DNA as template, but not with denatured or λDNA; (e) RNA molecules synthesized in its presence are of higher sedimentation value (10–20 S) than that synthesized in its absence (4 S); (f) it can completely counteract the inhibitory effect of rifampicin, which is known to inhibit RNA synthesis at the initiation step. Factor C seems to facilitate the release of synthesized RNA from the DNA template since (a) it stimulates RNA synthesis by polymerase CI when added on top of factor B, but in absence of factor B, C alone is inactive; (b) it can reinitiate RNA synthesis after the reaction has reached a plateau in a system where DNA is limiting, an affect similar to that obtained at higher ionic strength. Factor C, however, does not influence the molecular size of RNA synthesized. Furthermore, the RNA polymerase CI is sensitive to α‐amanitin whereas the RNA polymerase CII is comparatively resistant. The former appears to synthesize the non‐ribosomal RNA whereas the latter synthesizes ribosomal RNA.