Nucleotide sequence of dihydrofolate reductase type VI

Abstract

Summary. The complete sequence of the type VI dihydrofolate reductase (DHFR) gene from plasmid pUK672 was determined. The structural gene coded for a polypeptide of 157 amino acids which had a deduced mol. wt of 17 424. Comparison with amino-acid sequences of the type I, type V and Escherichia coli K12 chromosomal DHFRs showed that there was 63%, 61% and 3 1% homology respectively. Putative RNA polymerase and ribosomal binding sites were identified proximal to the initiation codon and a feature consistent with transcription termination was present distal to the coding region. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed that the enzyme had a subunit mol. wt of 17 500.

A novel dihydrofolate reductase cassette inserted in an integron borne on a Tn21-like element

“…In addition, the following leucine in E. coli enzyme is replaced by glutamine. These changes have previously been found among the family of highly resistant DHFRs, including types I, V, VI, and VII (18,45,52,55,61,62). On the other hand, at the phenotype level type XII DHFR showed properties distinct from those of these DHFRs.…”

“…DHFRs of types I, V, VI, and VII form a group of resistance enzymes with 61 to 75% amino acid sequence similarity (18,45,52,55,62). Type II DHFRs form another supergroup of DHFRs even more homologous with one another but with a structure distinct from that of any other known DHFR (7,14,50,57).…”

Gene cassettes: a new class of mobile element

“…6(a) (Recchia & Hall, 1995), and it is likely that further 'wild' cassettes will be found in the future. Indeed, one further potential example of a gene cassette located at a non-specific location is the 4 r A 6 gene (Wylie & Koornhof, 1991). Though the sequences flanking the dfrA6 gene do not resemble any known integron or gene cassette sequences, the DHFRVI protein belongs to the same subfamily as DHFRI, -V and -VII, all of which are encoded by cassette-associated genes, and a potential 59-base element containing inverted repeats and showing some similarity to the consensus for the outer ends of 59-base elements can be identified 3' to the dfrA6 gene (see Sundstrom et al, 1993).…”

Prevalence and genetic location of non-transferable trimethoprim resistant dihydrofolate reductase genes in South African commensal faecal isolates

“…Fifteen of these trimethoprim resistant enzymes have been identified in Enterobacteria and have been characterized according to their biochemistry and DNA sequence. They are the Ia [3], lb [4], Ila [5], Ilb [6], Ile [7], Illa [8], IIIb [9], IIIc [10] renamed the type VIII [11], IV [12], V [13], VI [14], VII [15], IX [16], X [17] and XII [18].…”