Cloning of the Haemophilus influenzae Dam methyltransferase and analysis of its relationship to the Dam methyltransferase encoded by the HP1 phage

In this paper we report cloning and experimental characterization of the DNA ade­nine methyltransferase (dam) gene from Haemophilus influenzae and comparison of its product with the Dam protein from the lysogenic phage of H. influenzae, HP1. Mo­lecular modeling of M.HinDam and M.HP1Dam was carried out, providing a frame­work for a comparative analysis of these enzymes and their close homologs in the structural context. Both proteins share the common fold and essential cofactor-bind- ing and catalytic residues despite overall divergence. However, subtle but significant differences in the cofactor-binding pocket have been identified. Moreover, while M.HinDam seems to contact its target DNA sequence using a number of loops, most of them are missing from M.HP1Dam. Analysis of both MTases suggests that their cata­lytic activity was derived from a common ancestor, but similar sequence specificities arose by convergence.