Practice question

SmaI, purified from Serratia marcescens, recognizes palindromic sequence 5'-CCC^GGG-3' and hydrolyzes phosphodiester bond between third cytosine and first guanine, denoted CCC^GGG, generating blunt-ended fragments lacking single-stranded extensions. Blunt-end ligation demands higher concentrations of T4 DNA ligase and conditions stabilizing ends, contrasting with efficient sticky-end ligation. SmaI sites are GC-rich and often located in CpG islands, and methylation of internal CpG at C5 can inhibit cleavage due to overlap with eukaryotic methylation patterns, influencing mapping and subcloning strategies in genomes and vectors.