Isolation and Sequencing of a Plant cDNA Encoding a Bifunctional Methylenetetrahydrofolate Dehydrogenase : Methenyltetrahydrofolate Cyclohydrolase Protein

Abstract

Summary In plant cells, the interconversion of formyl- and methylene-tetrahydrofolates is catalyzed by a bifunctional protein possessing methenyltetrallydrofolate cydohydrolase (EC 3.5.4.9) and methylenetetrahydrofolate dehydrogenase (EC 1.5.1.5) activities. The present work reports the isolation and sequencing of a cDNA that encodes this protein. Polydonal antibodies, raised against purified pea cytosolic dehydrogenase:cyclohydrolase, were used to screen a λgt 11 cDNA expression library, constructed from leaf extracts of this species. The screen identified a phage containing a cDNA insert with an open reading frame encoding a 294 amino acid protein (Mr 31,344). The deduced primary structure of this protein contained most of the conserved regions found in other dehydrogenase:cyclohydrolase proteins including the corresponding domains of the trifunctional C1-THF synthases of mammalian and yeast origins.