Nucleotide sequence of dihydrofolate reductase type VI

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 31% 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.