N-terminal domain of the Alpha subunit of Bacterial RNA polymerase
The bacterial alpha subunit of RNA polymerase (RNAP) consists of two independently folded domains: an amino-terminal domain (alphaNTD) and a carboxy-terminal domain (alphaCTD). AlphaCTD is not required for RNAP assembly but interacts with transcription activators. AlphaNTD is essential in vivo and in vitro for RNAP assembly and basal transcription. It is similar to the eukaryotic RPB3/AC40/archaeal D subunit, and contains two subdomains: one subdomain is similar the eukaryotic Rpb11/AC19/archaeal L subunit which is involved in dimerization; and the other is an inserted beta sheet subdomain. The alphaNTDs of plant plastid RNAP (PEP) are also included in this subfamily. PEP is largely responsible for the transcription of photosynthetic genes and is closely related to the multi-subunit bacterial RNAP, which is a large multi-subunit complex responsible for the synthesis of all bacterial RNAs. The bacterial RNAP core enzyme consists of four subunits (beta', beta, alpha and omega). All residues in the alpha subunit that is involved in dimerization or in the interaction with other subunits are located within alphaNTD.