As both arms are structured slightly differently, the subunits become conformationally tuned and thereby prepared for their respective role in the  recombination cycle. Contrary to members of the Tyr-class the recombination pathway converts two different substrate sites (attP and attB) to site-hybrids (attL and attR). This explains the irreversible nature of this particular recombination pathway, which can only be overcome by auxiliary "recombination directionality factors" (RDFs).]]
Both arms have slight structural differences, resulting in conformational tuning of subunits for their specific roles in the recombination cycle. Unlike members of the Tyr-class, the recombination process transforms two distinct substrate sites (attP and attB) into site-hybrids (attL and attR). This clarifies why this recombination pathway is irreversible and necessitates auxiliary "recombination directionality factors" (RDFs).