Initial TALEN studies used the wild - type FokI cleavage domain .
Some subsequent TALEN studies also used FokI cleavage domain variants with mutations designed to improve cleavage specificity and cleavage activity .
Initial TALEN studies used the wild - type FokI cleavage domain , but some subsequent TALEN studies also used FokI cleavage domain variants with mutations designed to improve cleavage specificity and cleavage activity .