The RNA polymerase II general elongation complex.

Eukaryotic messenger RNA (mRNA) synthesis is a complex multi-stage process that requires the concerted action of many cellular factors to generate a mature functional message. This elaborate process by RNA polymerase II (pol II) proceeds via multiple stages-preinitiation, initiation (Figure 1), promoter clearance, elongation (Figure 1) and termination - which have come to be referred to collectively as the transcription cycle. Although the preinitiation and initiation stages of transcription have received the most attention during the past decade, the past few years have been a watershed for biochemical studies of the pol II elongation complex. Recent studies have demonstrated the existence of several families of pol II elongation factors and nuclear proteins that can govern the activity of pol II during mRNA chain elongation. New findings have revealed that the elongation stage of transcription is a critical site for the regulation of gene expression. Evidence obtained to date suggests that eukaryotes regulate elongation by both 'general' and 'activator dependent' mechanisms. These mechanisms necessitate alteration of pol II's catalytic site, modification of chromatin structure, phosphorylation of the pol II carboxyl-terminal domain (CTD) and involvement of other components of the transcription machinery to increase the rate and efficiency of transcription elongation. This minireview is an annotation on the recent progress in studies of the biochemical mechanism and molecular regulation of the elongation stages of eukaryotic mRNA synthesis. The recent developments that have guided our understanding and propelled current research on transcription elongation by mammalian pol II will be described here.