Transcription by RNA polymerase II: initiator-directed formation of transcription-competent complexes

Studies of transcription by RNA polymerase II have revealed two promoter elements, the TATA motif and the initiator (Inr), capable of directing specific transcription initiation. Although binding to the TATA motif by one of the components of the transcription machinery has been shown to be the initial recognition step in transcription complex formation, many promoters that lack a traditional TATA motif have recently been described. In such TATA-less promoters, the Inr element is critical in positioning RNA polymerase II. Various Inr elements have been described and classified according to sequence homology. These Inr elements are recognized specifically by Inr-binding proteins. Interaction between these Inr-binding proteins and components of the basal transcription machinery provides a means through which a transcription competent complex can be formed.