Temperature-Sensitive Mutants of Escherichia coli K-12 with Low Activities of the l -Alanine Adding Enzyme and the d -Alanyl- d -Alanine Adding Enzyme

A number of properties of temperature-sensitive mutants in murein synthesis are described. The mutants grow at 30 C but lyse at 42 C. One mutant possesses a temperature-sensitive d-alanyl-d-alanine adding enzyme, has an impaired rate of murein synthesis in vivo at both 30 and 42 C, and contains elevated levels of uridine diphosphate-N-acetyl-muramyl-tripeptide (UDP-MurNAc-l-Ala-d-Glu-m-diaminopimelic acid) at 42 C. The other mutant possesses an l-alanine adding enzyme with a very low in vitro activity at both 30 and 42 C. Its in vivo rate of murein synthesis is almost normal at 30 C but is much less at 42 C. When the murein precursors were isolated after incubation of the cells in the presence of (14)C-l-alanine, they contained only a fraction of the radioactivity that could be obtained from a wild-type strain. A genetic nomenclature for genes concerned with murein synthesis is proposed.