The majority of proteins in this family consist of a single copy of this domain, though it is also found as a repeat. A strongly conserved histidine and a aspartate suggest that the domain has an enzymatic function. This family also now includes the family formerly known as the DGPF domain (COG3795). Although its function is unknown it is found fused to a sigma-70 factor family domain in CC_1329. Suggesting that this domain plays a role in transcription initiation (Bateman A per. obs.). This domain is named after the most conserved motif in the alignment.