dfp Gene of Escherichia coli K-12, a locus affecting DNA synthesis, codes for a flavoprotein

The cloned dfp gene complements dna-707 (now designated dfp-707), a temperature-sensitive conditionally lethal mutation that results in a slow cessation of DNA synthesis while protein synthesis is maintained. In vitro and in vivo experiments failed to demonstrate a specific defect in the initiation of DNA replication, and turn-off of DNA synthesis at high temperature was slower than that of a typical initiation (dnaA) mutant. The gene was localized, and its product was identified through the construction and analysis of deletion and insertion mutants of dfp-containing plasmids. dfp is located between the rpmB and dut genes at 81 min on the linkage map of Escherichia coli K-12. It is transcribed clockwise, independently of dut. The ability of a plasmid to complement a chromosomal dfp-707 mutation was correlated with its ability to produce a 45-kilodalton polypeptide. The purified protein contained 1 mol of flavin mononucleotide per mol of polypeptide.