The basic RNA polymerase II transcriptional machinery

Abstract

All genes encoding proteins in eukaryotes are transcribed by RNA polymerase II. The first step in analyzing transcriptional regulation requires understanding the general mechanisms of RNA polymerase II-specific gene transcription. The basal promoter, a template containing a TATA box devoid of upstream regulatory sequences, has been used to identify and characterize the factors which, together with RNA polymerase II, govern transcription in mammalian systems: TFIIA, TFIIB, TFIID, TFIIE, TFIIF, TFIIG, TFIIH, and TFIIJ. Interactions between regulatory transcription factors and basal elements of the transcriptional machinery affect the transcriptional rate in a positive or negative fashion. As these multiple proteins are purified, and their coding sequences are isolated, we come closer to reproducing these processes in vitro with pure components, and thus to elucidating the complex interactions among them.

Figure 1

Schematic representation of transcription initiation on the adenovirus 2 major late promoter (Ad2 MLP). The diagram summarizes data available as of October 10, 1991, and contains many modifications which are not fully described or attributed in the text, since not all of the data have been published. The location and role of some required factors, such as BTF-3 (Zheng et al., 1990), TFIIG (Sumimoto et al., 1990), or TFIIH (Flores et al., 1991), are less well characterized. The inverted G in step 9 indicates the 5′-5′ CAP dinucleotide formation, catalyzed by a guanosyltransferase that may also be associated with the transcription complex (Reinberg et al., 1987). Interactions with elongation factor SII or TFIIS (Rappaport et al., 1987, 1988) and the abortive initiation process (Luse and Jacob, 1987; Rougvie and Lis, 1988) or pausing (Resnekov and Aloni, 1989) are not discussed in this review. They do, however, point to areas of further study, and to the fate of transcription factors and RNA polymerase in recycling.