Two specific DNA binding sites for the enzyme dihydrofolate reductase from Lactobacillus casei have been located by means of an immunoprecipitation assay within a 2900-base pair L. casei DNA fragment containing the L. casei dihydrofolate reductase structural gene, which was previously cloned into pBR322. The inserted L. casei DNA was mapped using restriction endonucleases, and the location and ...

The disparate cross-resistance behavior of certain amethopterin-resistant Chinese hamster cell lines to the quinazoline antifolate, methasquin, prompted an investigation of the possibility of the existence of more than one species of dihydrofolate reducÃ-asein these cell populations. The dihydrofolate reductase of four amethopterin-resistant Chinese hamster sublines (DC-3F8/A50, 460-fold resist...

A fusion protein consisting of dihydrofolate reductase and diphtheria toxin A-fragment was made by genetically linking cDNA for the two proteins followed by in vitro transcription and translation in a rabbit reticulocyte lysate system. The dihydrofolate reductase in the fusion protein exhibited enzyme activity and, in the presence of methotrexate which imposes a tight structure on dihydrofolate...

The kinetic theory of substrate reaction during modification of enzyme activity has been applied to the study of inactivation kinetics of Chinese hamster dihydrofolate reductase by urea [Tsou (1988) Adv. Enzymol. Relat. Areas Mol. Biol. 61, 381-436]. On the basis of the kinetic equation of substrate reaction in the presence of urea, all microscopic kinetic constants for the free enzyme and enzy...

The folate analog, methotrexate, binds very tightly to dihydrofolate reductase. However, free intracellular methotrexate in excess of the enzyme-binding capacity is needed to suppress cellular dihydrofolate reduction, and the effects of methotrexate are rapidly reversible if methotrexate is removed from the extracellular media. The apparent paradox may be explained on the basis of a single high...

A strategy devised to isolate a gene coding for a dihydrofolate reductase from Thermus thermophilus DNA delivered only clones harboring instead a gene (the T. thermophilus dehydrogenase [DH(Tt)] gene) coding for a dihydropteridine reductase which displays considerable dihydrofolate reductase activity (about 20% of the activity detected with 6,7-dimethyl-7,8-dihydropterine in the quinonoid form ...

The implication of dihydrofolate reductase and dihydropteroate synthetase gene mutations in modification of Plasmodium falciparum characteristics Abstract Background: The Plasmodium falciparum dihydrofolate reductase (DHFR) and dihydropteroate synthetase (DHPS) are enzymes of central importance in parasite metabolism. The dhfr and dhps gene mutations are known to be associated with sulphadoxine...

A strain of Escherichia coli was isolated in which dihydrofolate reductase was not detected by an enzyme assay or by competition for antibody. This strain requires methionine, glycine, a purine, and thymidine for growth in addition to the auxotrophic requirements of the parent strain. It was found to be useful as a recipient of plasmids harboring dihydrofolate reductase genes.

Trimethoprim resistance dihydrofolate reductase genes from plasmids known to be exchanging between human and animal populations were mapped. The dihydrofolate reductase gene has been highly conserved in all plasmids, but differences in the flanking regions provide evidence that the most recent exchange of plasmids between the two ecosystems has been from animals to humans.

A new trimethoprim resistance determinant, designated dhfrX, was identified in the In7 integron of pDGO100. The sequence of the dhfrX dihydrofolate reductase is up to 28% identical to the sequences of several known dihydrofolate reductase proteins. The dhfrX gene is adjacent to the second 3'-conserved segment of the In7 integron, but the first 77 bases of this segment are not present.