Revealing secrets of the enigmatic omega subunit of bacterial RNA polymerase

The conserved omega (ω) subunit of RNA polymerase (RNAP) is the only nonessential subunit of bacterial RNAP core. The small ω subunit (7 kDa–11.5 kDa) contains three conserved α helices, and helices α2 and α3 contain five fully conserved amino acids of ω. Four conserved amino acids stabilize the correct folding of the ω subunit and one is located in the vicinity of the β′ subunit of RNAP. Otherwise ω shows high variation between bacterial taxa, and although the main interaction partner of ω is always β′, many interactions are taxon‐specific. ω‐less strains show pleiotropic phenotypes, and based on in vivo and in vitro results, a few roles for the ω subunits have been described. Interactions of the ω subunit with the β′ subunit are important for the RNAP core assembly and integrity. In addition, the ω subunit plays a role in promoter selection, as ω‐less RNAP cores recruit fewer primary σ factors and more alternative σ factors than intact RNAP cores in many species. Furthermore, the promoter selection of an ω‐less RNAP holoenzyme bearing the primary σ factor seems to differ from that of an intact RNAP holoenzyme.     

DNA-dependent RNA polymerase II from nuclei of suspension-cultured tobacco cells

From isolated nuclei of suspension cultured cells of Nicotiana tabacum. DNA-dependent RNA polymerase II (E.C. 2.7.76) has been purified to homogeneity as evidenced by polyacrylamidegel electrophoresis under non-denaturing conditions. The purified enzyme had a specific activity of more than 15 nmol min^-1·mg^-1 with denatured calf thymus DNA as template. Sodium-dodecyl-sulfate gel electrophoresis and protein highperformance liquid chromatography revealed a subunit composition of four proteins with molecular weights of 165 000, 135 000, 35 000 and 25 000 and with a stoichiometry of 1:1:2:2. The RNA polymerase did not exhibit any detectable proteinkinase activity. The 25 000 subunit binds ADP in a molar ratio of 1:1; it could not be decided whether this subunit has an ATPase activity or is merely an acceptor of ADP.Abbreviations HPLC high-performance liquid chromatography - PMSF phenylmethylsulfonyl fluoride - SDS sodium dodecyl sulfate This contribution is dedicated to Professor Fritz Cramer on the occasion of his 60th birthday