In mammalian cells reiterated binding sites for Sp1 and two overlapping and inverted E2F sites at the transcription start site regulate the dhfr promoter during the cell growth cycle. Here we have examined the contributions of the dhfr Sp1 and E2F sites in the repression of dhfr gene expression. In serum-starved cells or during serum stimulation, the Chinese hamster dhfr gene was not derepresse...

BACKGROUND Dihydrofolate reductase (DHFR) converts dihydrofolate (DHF) into tetrahydrofolate (THF) and plays an essential role in cell metabolism and cellular growth. Folic acid from multivitamins needs to be reduced by DHFR before it participates in cellular reactions. OBJECTIVES We examined the relation of a 19-base pair (bp) deletion polymorphism of the DHFR gene with the risk of breast ca...

We have determined the nucleotide sequence of the dihydrofolate reductase-thymidylate synthetase (DHFR-TS) gene of the protozoan parasite Leishmania major (dihydrofolate reductase, EC 1.5.1.3 and thymidylate synthase, EC 2.1.1.45). The DHFR-TS protein is encoded by a single 1560-base-pair open reading frame within genomic DNA, in contrast to vertebrate DHFRs or mouse and phage T4 TSs, which con...

This study examined polymorphisms in the dihydrofolate reductase (DHFR) gene of Pneumocystis carinii isolates from 27 patients with P. carinii pneumonia (PCP) in Japan. Four substitution sites with two synonymous and two non-synonymous changes were found. Two synonymous substitutions at nucleotide positions 540 and 312 were identified in one and 13 patients, respectively. Two amino acid substit...

Cultured human KB cells which developed resistance to increasing concentrations of methotrexate showed increased levels of dihydrofolate reductase (DHFR) as demonstrated by an immunobridge staining technique. Peripheral blast cells from a leukemic patient were examined for DHFR content during several courses of methotrexate therapy. The number of cells which demonstrated high levels of DHFR inc...

Among a collection of clinical Escherichia coli isolates, the type I dihydrofolate reductase (DHFR) mediating trimethoprim resistance was generally observed to be chromosomally determined. Only a minority of isolates carried the type I DHFR gene simultaneously on a plasmid. The majority of E. coli isolates studied also hybridized with a probe specific for the transposition gene tnsC of transpos...

DHFR (dihydrofolate reductase) catalyses the metabolically important reduction of 7,8-dihydrofolate by NADPH. DHFR from the hyperthermophilic bacterium Thermotoga maritima (TmDHFR), which shares similarity with DHFR from Escherichia coli, has previously been characterized structurally. Its tertiary structure is similar to that of DHFR from E. coli but it is the only DHFR characterized so far th...

R67 dihydrofolate reductase (DHFR), encoded by an R plasmid, provides resistance to the antibacterial drug trimethoprim. This enzyme does not exhibit any structural or sequence homologies with chromosomal DHFR. A recent crystal structure of tetrameric R67 DHFR (D. Matthews, X. Nguyen-huu, and N. Narayana, personal communication) shows a single pore traversing the length of the molecule. Numerou...

The chromosomal location of the human dihydrofolate reductase (DHFR; EC 1.5.1.3) gene that is amplified in a methotrexate-resistant human cell line has been investigated by screening a large number of human-mouse cell hybrids containing overlapping subsets of human chromosomes. A correlation of genomic blotting data with the chromosome constitution of the individual cell hybrids has allowed the...

Three independently-derived, antifolate-resistant Chinese hamster lung cell lines that exhibit low level increases in dihydrofolate reductase (DHFR) activity, i.e., three- to fivefold vs. controls, have been compared with drug-sensitive cells to determine relative DHFR gene content. With a solution hybridization technique that makes use of genomic DNA and a cloned double-stranded Chinese hamste...