Total DNA of the archaebacterium Methanococcus vannielii was digested with BamHI or BamHI/HindIII, cloned with plasmid Yip5 and analyzed for sequences capable of autonomous replication (ARSs) in the eukaryote Saccharomyces cerevisiae. Two recombinant plasmids were isolated which contained 3.3 kb and 8 kb fragments of methanogen derived DNA with ARS activity. They exhibited low transformation efficiencies for yeast and promoted slow growth of yeast transformants.