Distinctive multiple thymidine kinase species of the aquatic filamentous fungus Achlya ambisexualis

Abstract

Four thymidine kinase (TK) species were found in the cell extract of the filamentous fungus Achyla ambisexualis. They differed by their relative electrophoretic mobilities (Rm) on polyacrylamide gel in nondenaturing buffer and are designated as the Rm 0.30, 0.45, 0.65, and 0.85 TK species. The Rm 0.30 activity was readily solubilized from the mycelia by freeze–thaw treatment, whereas the other TK species were solubilized by additional treatment with nonionic detergent nonidet P-40. The Rm 0.30, 0.65, and 0.85 TK species utilized only ATP as a phosphate donor and dT as a phosphate acceptor. However, the Rm 0.45 species utilized all four ribonucleoside triphosphates as phosphate donors and dC, in addition to dT, as phosphate acceptors. Therefore, this TK species is a deoxypyrimidine kinase. All four TK activities were inhibited by the feedback inhibitor dTTP. However, only the Rm 0.45 TK activity was inhibited by dCTP. The characterization of distinctive multiple TK species in A. ambisexualis will facilitate the studies using this fungus as a transformation host cell for vectors carrying TK as a reported gene.