Practice question

SalI is a Type II restriction endonuclease isolated from Streptomyces albus that recognizes palindromic hexamer 5'-G^TCGAC-3' and cleaves between G and TCGAC to generate four-nucleotide 5' overhang with sequence TCGA. The staggered cut produces cohesive termini that anneal efficiently, enabling ligation with other fragments sharing TCGA overhangs, notably those produced by XhoI. Cleavage requires magnesium as cofactor and is inhibited if the recognition site overlaps Dam-methylated GATC leading to methylation-dependent blockage. SalI remains widely used for mapping large plasmids, constructing genomic libraries, and directional subcloning applications.