ABSTRACT
The formation of eukaryotic messenger ribonucleic acid (mRNA) involves a complex series of enzyme-catalyzed biochemical reactions. Cellular mRNAs are capped and methylated in a series of reactions very similar to those proposed for vaccinia and reovirus. However, some important differences exist in the enzymes involved in the reactions. Isolation and characterization of the enzymes responsible for cap formation have significantly increased our understanding of the sequence of cellular events. Vaccinia and reovirus mRNAs are capped and methylated in a series of reactions very similar to the initial reactions proposed for cellular mRNA. However, in contrast to the cellular capping enzymes, the vaccinia virus RNA triphosphatase, RNA guanylyltransferase, and RNA guanine-7-methyltransferase are tightly associated in a multifunctional enzyme complex. A variation in the methylation of the terminal guanosine residue has been identified in blocked 5'-ends of low-molecular-weight nuclear RNAs from Novikoff hepatoma cells.
