SmaI is a type II restriction enzyme; it is an isoschizomer of XmaI. SmaI produces blunt-ended fragments whereas XmaI produces a 5´ overhang. SmaI is unusual in that it shows maximal activity at 25 °C; it has a half-life of 15 minutes at 37 °C, which is the incubation temperature used for most restriction enzymes.
5' - C C C ↓ G G G 3'
3' - G G G ↑ C C C 5'.