Enzymes of deoxythymidine triphosphate biosynthesis in Neurospora crassa mitochondria.

Intact mitochondria of Neurospora crassa incorporate deoxythymidine 5'-monophosphate (dTMP) into deoxyribonucleic acid but not the label from (methyl-3H) deoxythymidine. Mitochondrial homogenates contain deoxythymidylate kinase (EC 2.7.4.9), deoxycytidylate aminohydrolase (dCMP deaminase) (EC 3.5.4.12), and thymidylate synthetase (EC 2.1.1b), but not thymidine kinase (EC 2.7.1.21) activity. dTMP kinase is loosely bound to the mitochondrial membrane and is solubilized by 0.4 M KCl in mitochondrial homogenates, the dCMP aminohydrolase deaminase) is bound to the inner membrane and is not solubilized by 0.4 M KCl. dTMP synthetase activity is found in the 2,000 times g particulate fractions by homogenization of mitochondria in 0.4 M KCl. The dCMP deaminase activity found in the particulate fraction of the inner membrane is efficiently regulated by the products of the pathway: deoxycytidine 5'-triphosphate activates whereas deoxythymidine 5'-triphosphate inhibits, as found for the soluble enzyme from other sources. These data indicate that mitochondria of N. crassa contain specific enzymes for the biosynthesis of deoxythymidine triphosphate.     

The prebiotic synthesis of deoxythymidine oligonucleotides

Summary A reaction shown to oligomerize nucleotides under possible prebiotic conditions has been made more plausible by the finding that the reaction can proceed at initial neutral pH in the presence of acid salts or NH₄Cl.     

The prebiotic synthesis of deoxythymidine oligonucleotides

A reaction which oligomerizes nucleotides under possible prebiotic conditions has been characterized. Nucleoside monophosphate in the presence of cyanamide at acid pH condenses to form dithymideine pyrophosphate and phosphodiester bonded compounds. Imidazole compounds and activated precursors such as nucleoside triphosphate are not necessary for this ologomerization reaction which produces primarily cyclic ologonucleotides.     

Biochemical transformation of deoxythymidine kinase-deficient mouse cells with UV-irradiated equine herpesvirus type 1.

A line of 3T3 mouse cells lacking deoxythymidine kinase (dTK-) was stably transformed to the dTK+ phenotype after exposure to UV-irradiated equine herpesvirus type 1 (EHV-1). Biochemical transformants were isolated in a system selective for the dTK+ phenotype (Eagle minimal essential medium containing 10(-4) M hypoxanthine, 6 X 10(-7) M aminopterin, and 2 X 10(-5) M deoxythymidine). Transformation was accompanied by the acquisition of a dTK activity with immunological, electrophoretic, and biochemical characteristics identical to those of the dTK induced by EHV-1 during productive infection. The transformed cells have been maintained in selective culture medium for more than 50 passages and have retained the capacity to express EHV-1--specific antigens. Spontaneous release of infectious virus has not been detected in the transformed lines, and the the cells were not oncogenic for athymic nude mice. In contrast to normal dTk+ 3T3 cells, EHV-1 transformants were unable to grow in the presence of arabinosylthymine, a drug selectively phosphorylated by herpesvirus-coded dTK's. These results indicate that a portion of the EHV-1 genome is able to persist in the transformed cells for many generations and be expressed as an enzymatically active viral gene product.     

Mutation induction in yeast by deoxythymidine monophosphate: A model

Summary High concentrations of deoxythymidine monophosphate (dTMP) induce mutations in Saccharomyces cerevisiae. Strains defective in the RAD6 gene-thought to be involved in error-prone DNA repair-do not show dTMP-induced mutation. We propose a model to explain these findings and suggest that fluxes of thymidine nucleotides may diminish the fidelity of DNA replication.     

The yeast Cdc8 exhibits both deoxythymidine monophosphate and diphosphate kinase activities

The existence of multifunctional enzymes in the nucleotide biosynthesis pathways is believed to be one of the important mechanisms to facilitate the synthesis and the efficient supply of deoxyribonucleotides for DNA replication. Here, we used the bacterially expressed yeast thymidylate kinase (encoded by the CDC8 gene) to demonstrate that the purified Cdc8 protein possessed thymidylate-specific nucleoside diphosphate kinase activity in addition to thymidylate kinase activity. The yeast endogenous nucleoside diphosphate kinase is encoded by YNK1, which appears to be non-essential. Our results suggest that Cdc8 has dual enzyme activities and could duplicate the function of Ynk1 in thymidylate synthesis. We also discuss the importance of the coordinated expression of CDC8 during the cell cycle progression in yeast.