Isolation and mutation site determination of the temperature-sensitive murB mutants of Staphylococcus aureus

The murB gene encodes UDP-N-acetylenolpyruvylglucosamine reductase and functions in bacterial peptidoglycan biosynthesis. A plasmid carrying the murB gene restored the temperature-sensitive growth of six Staphylococcus aureus mutants, in which peptidoglycan biosynthesis stopped at a restrictive temperature. Specific activity of UDP-N-acetylenolpyruvylglucosamine reductase in extracts from the mutants was lower than that from wild-type cells. Nucleotide sequence determination revealed that each mutant had a single amino acid substitution in the murB gene and five of six mutations were located within domain 3, where the proposed substrate binding site is located. These results suggest that the murB gene is essential for growth of S. aureus and that domain 3 is important for the MurB activity.