This chapter discusses the initiation of transcription of protein-coding genes. The RNA polymerase II(RNAPII) of the yeast Saccharomyces cerevisiae has been a useful prototype in the study of eukaryotic RNAPII, as features such as function and subunit structure have been highly conserved. The yeast RNAPII is composed of 11 polypeptides with apparent masses ranging from 220 to 10 kDa. This is in contrast to eukaryotic cells, which contain three distinct RNA polymerases, each containing from 8 to 14 polypeptides and responsible for transcribing its own set of genes: RNA polymerase I (RNAPI), which transcribes ribosomal RNA; RNAPII, the RNA polymerase of protein-coding, or class 11, genes; and RNAPIII, which transcribes 5-S rRNA and tRNA genes. In this chapter, only RNAPII is discussed, and only as it pertains to transcription initiation. © 1993 Academic Press Inc.