The quaternary structure of DNA-dependent RNA polymerase

The crystals of RNA polymerase of T. thermophilus were examined by electron microscopic observation of the negatively stained and sectioned materials. Three types of crystals were observed: ordered aggregates (Type I), cylindrical duplei (Type II), and plane (Type III) forms. It was deduced mainly from sectioned images that Type I crystal is a precursor or a premature form of Type II crystal. The III corresponds to the flattened layer of type II. In Type II crystal the enzyme molecules are arranged in an orderly two-dimensional lattice and thus we could analyze the molecular structure by optical filtering of the negatively stained images. On the basis of these results, a quaternary structure is proposed for RNA polymerase.