The genes encoding the acetate kinase and phosphotransacetylase enzymes from <i>Methanosarcina thermophila</i> were isolated from a genomic library on a fifteen kilobase fragment The genes are located adjacent to one another, with the phosphotransacetylase gene (<i>pta</i>) directly upstream of the acetate kinase gene (<i>ack</i>). The two genes were sequenced, along with a third Open Reading Frame (designated <i>orfY</i>). The <i>orfY</i> gene appears to encode a novel protein whose physiological function has yet to be determined. / Ph. D.