The ACS is an 11-bp sequence of the form 5'-WTTTAYRTTTW-3' which is at the core of every yeast ARS, and is necessary but not sufficient for recognition and binding by the origin recognition complex (ORC). Functional ARSs require an ACS, as well as other cis elements in the 5' (C domain) and 3' (B domain) flanking sequences of the ACS.