Sequence of the fifth largest subunit of RNA polymerase II from plants

An affinity-purified antibody raised against the fifth largest subunit of cauliflower (Brassica oleracea) RNA polymerase II was used to screen an expression library and isolate an Arabidopsis thaliana cDNA clone. This cDNA clone was used to isolate a soybean (Glycine max) cDNA clone, and both clones were sequenced. The open reading frames contain 176 amino acids and predict polypeptides of 19.5 and 19.6 kDa for Arabidopsis and soybean, respectively. The amino acid sequences of the Arabidopsis and soybean polypeptides are 91.5% identical. The fifth largest subunit in plant RNA polymerase II is present at unit stoichiometry in purified enzyme and does not dissociate from the holoenzyme during nondenaturing polyacrylamide gel electrophoresis. The gene encoding the 19.5-kDa subunit has been isolated and sequenced from Arabidopsis. The gene is single copy and contains five introns. The size of the mRNA encoding this RNA polymerase II subunit in Arabidopsis and soybean is approximately 1 kilobase. None of the published yeast or animal RNA polymerase subunit sequences show similarity to the fifth largest subunit in plants.