title: Protein expression in Escherichia coli minicells containing recombinant plasmids specifying trimethoprim-resistant dihydrofolate reductases.
abstract: Deoxyribonucleic acid fragments containing the structural genes for several trimethoprim-resistant dihydrofolate reductases from naturally occurring plasmids were inserted into small cloning vehicles. The genetic expression of these hybrid plasmids was studied in purified Escherichia coli minicells. The type I dihydrofolate reductase, encoded by plasmid R483 and residing within transposon 7 (Tn7), had a subunit molecular weight of 18,000. The type II dihydrofolate reductase, specified by plasmid R67, had a subunit molecular weight of 9,000. These two enzymes were antigenically distinct in that anti-type II dihydrofolate reductase (R67) antibody did not cross-react with the type I (R483) protein. The trimethoprim-resistant reductase specified by plasmid R388 had a subunit molecular weight of about 10,500 and was immunologically related to the type II (R67) enzyme. A 9,000 subunit of the dihydrofolate encoded by the transposition element Tn402 was also antigenically related to the R67 reductase.
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis*; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D008970:Molecular Weight; D010452:Peptide Biosynthesis; D010957:Plasmids; D011815:R Factors; D011995:Recombination, Genetic; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics* / Q000378:metabolism; D014295:Trimethoprim / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D014295:Trimethoprim; D013762:Tetrahydrofolate Dehydrogenase