Cloning of a cDNA for the S-adenosyl-L-homocysteine hydrolase from Dictyostelium discoideum.

We screened a cDNA library of the primitive eukaryote Dictyostelium discoideum constructed in the expression vector lambda gt11 with a specific antiserum directed against S-adenosyl-L-homocysteine hydrolase (AdoHcy hydrolase) and isolated cDNA clones coding for fusion proteins with beta-galactosidase. The identity of the largest of these clones was further assessed by analysis of hybrid-selected in vitro translation products. Using the cDNA as a probe, we showed that only one gene coding for AdoHcy hydrolase is present per genome and that a single transcript of 1.6 kb could be detected at various stages of differentiation. The nucleotide sequence of the cDNA was determined. It corresponds to the carboxyterminal half of the protein whose primary structure is highly homologous to the AdoHcy hydrolase from rat liver. The significance of this strong conservation of AdoHcy hydrolase in the course of evolution is discussed.