| Abstract: | The regulation of macromolecular biosynthesis was studied in a temperature-sensitive mutant of Escherichia coli previously identified as containing a single mutation causing a thermolabile sn-glycerol-3-phosphate acyltransferase, the first enzyme of the pathway for phospholipid biosynthesis. When this mutant was shifted to a nonpermissive temperature, phospholipid synthesis, as well as ribonucleic acid, deoxyribonucleic acid, and protein synthesis, decreased in a coordinate manner, suggesting the existence of a common regulatory mechanism. During the same time that the rate of macromolecular synthesis was decreasing at the nonpermissive temperature, the intracellular concentration of adenosine 5'-triphosphate dropped dramatically and the concentration of adenosine monophosphate increased. The concentration of adenosine 5'-diphosphate dropped, but not as markedly. The decrease in macromolecular synthesis and the changes in the adenine nucleotide concentrations can now be attributed to a thermolabile adenylate kinase. The inactivation of adenylate kinase prevented the cell from converting adenosine 5'-monophosphate to adenosine 5'-diphosphate and consequently from making adenosine 5'-triphosphate. This in turn caused a decrease in the rate of macromolecular synthesis and cell growth. Adenylate kinase, therefore, is a key enzyme in controlling the rate of cell growth. The nature of the possible relationship between adenylate kinase and glycerol-3-phosphate acyltransferase is discussed. |
