RNA polymerases catalyse the DNA dependent polymerisation of RNA. Prokaryotes contain a single RNA polymerase compared to three in eukaryotes (not including mitochondrial. and chloroplast polymerases). This domain, domain 6, represents a mobile module of the RNA polymerase. Domain 6 forms part of the shelf module [1,2]. This family appears to be specific to the largest subunit of RNA polymerase II.

1: Structural modules of the large subunits of RNA polymerase. Introducing archaebacterial and chloroplast split sites in the beta and beta' subunits of Escherichia coli RNA polymerase. Severinov K, Mustaev A, Kukarin A, Muzzin O, Bass I, Darst SA, Goldfarb A; J Biol Chem 1996;271:27969-27974. PMID:8910400

2: Structural basis of transcription: RNA polymerase II at 2.8 angstrom resolution. Cramer P, Bushnell DA, Kornberg RD; Science 2001;292:1863-1876. PMID:11313498