ARS sequences in homologous and heterologous ADE2 loci are capable of promoting autonomous replication of plasmids in Schwanniomyces occidentalis

We have analyzed ARS elements linked to homologous and heterologous ADE2 loci functioning in Schwanniomyces occidentalis. We have identified a region of the ADE2 locus of S. occidentalis which promotes autonomous replication of plasmids in S. occidentalis cells. This region is within 385 bp preceding the ATG codon of the S. occidentalis ADE2 gene. It contains sequences similar to ARS core consensus sequences, ARS boxes, and a potential transcription activator binding site characterized in Saccharomyces cerevisiae. The ADE2 gene of S. cerevisiae was found to complement the ade2 mutation in S. occidentalis cells and the 5' UTR region of this gene is capable of supporting autonomous replication of plasmids in S. occidentalis. Furthermore, we confirmed that the origin of replication of the 2 microm plasmid and the ARS1 sequence of S. cerevisiae are also functional in S. occidentalis cells. Plasmids carrying either ARS, the SwARSA element of S. occidentalis, the ARS linked to the ADE2 gene of S. cerevisiae, and the ARS1 sequence or the 2 microm ori, were found to be maintained in S. occidentalis cells as episomal monomers or oligomers. However, their stability was low as already reported for the ARS in S. occidentalis.