Key Concepts rna polymerase i synthesizes rrNa in the nucleolus RNa polymerase ii synthesizes mrNa in the nucleoplasm RNa polymerase III synthesizes small RNAS in the nucleoplasm The largest subunit in rna polymerase ll has a Ctd(carboxy-terminal domain) consisting of multiple repeats of a septamerKey Concepts • RNA polymerase I synthesizes rRNA in the nucleolus • RNA polymerase II synthesizes mRNA in the nucleoplasm • RNA polymerase III synthesizes small RNAs in the nucleoplasm • The largest subunit in RNA polymerase II has a CTD (carboxy-terminal domain) consisting of multiple repeats of a septamer