This is a family of bacterial proteins that have a nucleotidyltransferase fold. The fold-prediction is backed up by conservation of three highly characteristic sequence motifs found in all other nucleotidyl transferases: i) pDhDhhh(h/p), where p is a polar residue and h is a hydrophobic residue; ii) upstream of the first, a GG/S; iii) a conserved D/E in a hydrophobic surround. In the classification of nucleotidyltransferases proposed in this is a group XVIII NTP-transferase. Many of these sequences were classified in the COG database as COG5397. The exact function is not known.