This group of 2H-phosphodiesterases comprises a single family typified by the protein mlr3352 from M.loti. Members are also present in various alpha-proteobacteria, Synechocystis, Streptococcus and Chilo iridescent virus. The presence of a member of this predominantly bacterial group in a large eukaryotic DNA virus represents a potential case of horizontal transfer from a bacterial source into a virus. Several proteins of bacterial origin have been noticed in the insect viruses (L.M.Iyer, E.V.Koonin and L.Aravind, unpublished observations and these appear to have been acquired from endo-symbiotic or parasitic bacteria that share the same host cells with the viruses. Presence of 2H proteins in the proteomes of large DNA viruses (e.g. T4 57B protein and the Fowl-pox virus FPV025) may point to some role for these proteins in regulating the viral tRNA metabolism. Each member of this family contains an internal duplication, each of which contains an HXTX motif that defines the family.