BIOCHEMICAL-EVIDENCE FOR THE PRESENCE OF A BIFUNCTIONAL DIHYDROFOLATEREDUCTASE-THYMIDYLATE SYNTHASE IN PLANT-SPECIES

It is shown that wild carrot cells contain both a bifunctional DHFR-TS (EC 2.1.1.45)land a monofunctional DHFR (EC 1.5.1.3). The bifunctiona l protein was present as the major DHFR fraction (80%) eluted from MTX -Sepharose. SDS-PAGE and immunoblot experiments showed that wild and d omesticated carrot DHFR-TS have the same molecular mass (about 58 kDa) . The immunochemical analysis showed the occurrence of the 58 kDa poly peptide also in the Nicotiana plumbaginifolia MTX-Sepharose fraction, whereas a band of about 50 kDa was recognized in Oryza sativa. DHFR an d TS activities were present in both purified fractions. These data in dicate that the bifunctional DHFR-TS is ubiquitous in plant cells.