An Mrr-family nuclease motif in the single polypeptide restriction-modification enzyme LlaGI.
Bioinformatic analysis of the putative nuclease domain of the single polypeptide restriction-modification enzyme LlaGI reveals amino acid motifs characteristic of the Escherichia coli methylated DNA-specific Mrr endonuclease. Using mutagenesis, we examined the role of the conserved residues in both DNA translocation and cleavage. Mutations in those residues predicted to play a role in DNA hydrolysis produced enzymes that could translocate on DNA but were either unable to cleave the polynucleotide track or had reduced nuclease activity. Cleavage by LlaGI is not targeted to methylated DNA, suggesting that the conserved motifs in the Mrr domain are a conventional sub-family of the PD-(D/E)XK superfamily of DNA nucleases.
DNA-Protein Interactions Unit, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol, BS8 1TD, UK.
Rachel M
RM
Smith
Jytte
J
Josephsen
Mark D
MD
Szczelkun
D020816:Amino Acid Motifs; D004247:DNA / Q000378:metabolism; D053837:DNA Cleavage; D004262:DNA Restriction Enzymes / Q000737:chemistry; D015280:DNA Restriction-Modification Enzymes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry; D016296:Mutagenesis; D017434:Protein Structure, Tertiary
D015280:DNA Restriction-Modification Enzymes; D029968:Escherichia coli Proteins; C431608:LlaGI restriction-modification system; D004247:DNA; D004262:DNA Restriction Enzymes; C070141:Mrr protein, E coli