ARS Vectors - In yeast chromosomes, origin of replication is specified by about 100 bp sequences called autonomously replicating sequences (ARS). All ARS sequences have a 11 bp consensus sequence, which is essential for their function; other functional but variable sequences are also present in ARS. Any DNA double helix containing an ARS can serve as a yeast vector.

Such a vector will be maintained in yeast cells only if it is essential for their survival, e.g., is the only source of an essential gene (say, TRP 1) in yeast cells mutant for that gene (in this case, Trp1- yeast cells). But in the absence of such a selection pressure ARS vectors are rapidly lost.