SmaI

SmaI is a restriction enzyme isolated from Serratia marcescens. It is a type I restriction enzyme, meaning it possesses both restriction and modification activities within a single protein complex. SmaI recognizes the palindromic DNA sequence CCCGGG and cleaves at a distance of 7 base pairs from the recognition site, resulting in a staggered cut. The enzyme requires S-adenosylmethionine (SAM), ATP, and magnesium ions as cofactors for its activity. Because it is a type I enzyme, SmaI is less commonly used in molecular biology applications compared to type II restriction enzymes which cleave within their recognition site. The modification activity of SmaI methylates the internal cytosine residues of the recognition sequence, specifically forming 5-methylcytosine. This methylation protects the DNA from cleavage by the enzyme. Understanding the cleavage and modification patterns of SmaI is important for DNA manipulation techniques that involve its specific recognition sequence.