The Control of Ribonucleic Acid Synthesis in Escherichia coli

The preceding paper in this series presented evidence implicating an unusual phosphorylated compound (MS I) as a possible inhibitor of RNA accumulation during amino acid starvation of stringent strains of Escherichia coli. Here a method is described for isolating MS I from batch cultures of a stringent valyl transfer RNA synthetase mutant. Chemical analyses indicate that MS I is a tetraphosphate of guanosine. However, in contrast to previously described isomers of guanosine tetraphosphate (ppppG and pppGp), MS I is labile in alkali. Charge considerations, enzyme degradation studies, and labilities in acid and alkali lead to a structural assignment for MS I of guanosine 5'-diphosphate or 3'- or 2'-diphosphate (ppGpp).