The ends of the affair: Capping and polyadenylation

Nearly all mRNAs are post-transcriptionally modified at their 5' and 3' end s, by capping and polyadenylation, respectively. These essential modificati ons are of course chemically quite distinct, as are the enzymatic complexes responsible for their synthesis. But recent studies have uncovered some si milarities as well. For example, both involve entirely protein machinery, w hich is now the exception rather than the rule in RNA processing and modifi cation reactions, and the two reactions share one important factor, namely RNA polymerase II. In this brief review, we describe progress in understand ing the enzymes and factors that participate in these two processes, highli ghting the evolutionary conservation, from yeast to humans, that has become apparent.