Studies on the functions of the RNA polymerase components by means of mutations

Summary It had been shown earlier, that RNA polymerase 13 S particles contain the large components with a molecular weight of about 3–10⁵ and small subunits with a molecular weight of 4·10⁴-1·10⁵. These polymerase components easily dissociate and reassociate with restoration of the enzyme activity.Both temperature-sensitive (tsX) and rifamycin-resistant (rif-r-I) mutations proved to affect the large polymerase component without changing the small subunits. These mutations were mapped at different, though closely linked, loci of metB-thi region of E. coli K12 chromosome. These results as well as certain literature data allow to conclude that the large RNA polymerase component consists of at least two polypeptides, one being altered by ts mutation, and the other—by rif-r mutation.The large polymerase component when separated from the small subunits retain the ability to bind to T2 phage DNA while the separate small subunits lack this property. Rifamycin does not affect RNA polymerase-T2 DNA binding while ts mutation leads to inability of the enzyme to form stable complexes with DNA. Therefore, it is likely that the polypeptide affected by ts mutation is responsible for the attachment of RNA polymerase to specific sites of DNA template. On the other hand, the small subunits as well as polypeptide of the large component, which determines RNA polymerase sensitivity to rifamycin, seem not to participate in the enzyme binding to DNA template. It is suggested, that the catalytic site of RNA polymerase is located in the large component and formed by rifamycin-binding polypeptide. The small subunits are supposed to have regulatory function and activate the large components.