5'-CAPPING ENZYMES ARE TARGETED TO PRE-MESSENGER-RNA BY BINDING TO THE PHOSPHORYLATED CARBOXY-TERMINAL DOMAIN OF RNA-POLYMERASE-II

We have investigated the role of the RNA Polymerase ZI (Pol ZI) carbox y-terminal domain (CTD) in mRNA 5' capping. Transcripts made in vivo b y Pol II with a truncated CTD had a lower proportion of capped 5' ends than those made by Pol II with a full-length CTD. In addition, the en zymes responsible for cap synthesis, RNA guanylyltransferase, and RNA (guanine-7)-methyltransferase bound directly to the phosphorylated, bu t not to the nonphosphorylated, form of the CTD in vitro. These result s suggest that: (1) Pol II-specific capping of nascent transcripts in vivo is enhanced by recruitment of the capping enzymes to the CTD and (2) capping is co-ordinated with CTD phosphorylation.