CLONING AND CHARACTERIZATION OF THE GENE ENCODING PSPPI METHYLTRANSFERASE FROM THE ANTARCTIC PSYCHROTROPH PSYCHROBACTER SP. STRAIN TA137 - PREDICTED INTERACTIONS WITH DNA AND ORGANIZATION OF THE VARIABLE REGION

The gene (pspPIM) encoding the PspPI DNA methyltransferase (MTase) ass ociated with the PspPI restriction-modification (R-M) system (5'-GGNCC -3') of Psychrobacter species TA137 has been cloned and expressed in E . coli, and its nucleotide (nt) sequence has been determined. The codi ng region was 1248 nt in length and capable of specifying a 46 826-Da protein of 416 amino acids (aa). The predicted sequence of the MTase p rotein displays ten sequence motifs characteristic of all prokaryotic m(5)C-MTases and shows the highest similarity to other MTases that met hylate the GGNCC sequence, namely M.Eco47II and M.Sau96I. All three MT ases methylate the internal cytosine within their recognition sequence . Sequence similarities between M.PspPI and its isospecific M.Eco47II and M.Sau96I as well as with four other m(5)C-MTases that methylate th e related GGWCC sequence, namely M.SinI, M.HgiCII, M.HgiBI, M.HgiEI ha ve been also found within the variable region of these proteins. On th e basis of structural information from M.HhaI and M.HaeIII, several M. PspPI residues that are expected to interact with DNA can be predicted . Furthermore, an organization of the variable region of m(5)C-MTases into two segments exhibiting a pattern of conserved residues and a con siderable degree of structural homologies is described. (C) 1997 Elsev ier Science B.V.