ScoMcrA is a type IV modification-dependent restriction endonuclease found in the model strain Streptomyces coelicolor. Unlike type I, II and III restriction endonucleases, which cleave unmodified DNA, type IV restriction endonucleases cleave modified DNA, including methylated, hydroxymethylated, glucosyl-hydroxymethylated and phosphorothioated DNA. ScoMcrA targets both Dcm-methylated DNA and phosphorothioated DNA, and makes double-strand breaks 16-28 nt away from the modified nucleotides or the phosphorothioate links. However, the mechanism by which ScoMcrA recognizes these two entirely different types of modification remains unclear. In this study, the ScoMcrA protein was overexpressed, purified and crystallized. The crystals diffracted to 3.35 Å resolution and belonged to space group P2(1)2(1)2(1). The unit-cell parameters were determined to be a=130.19, b=139.36, c=281.01 Å, α=β=γ=90°. These results will facilitate the detailed structural analysis of ScoMcrA and further elucidation of its biochemical mechanism.
Keywords: DNA phosphorothioation; Dcm methylation; ScoMcrA.