recombination attachment site attL Meng LIU (Mia), Oliver He https://academic.oup.com/femsre/article/41/4/512/3089980 The integration reaction is catalyzed by the integrase and, as a result of the site-specific recombination, will lead to direct repeats (typically between 10 and 60 bp) forming on either end of the integrated element, that are now named attL (left end) and attR (right end).