Arginine control of transcription of argECBH messenger ribonucleic acid in Escherichia coli

Abstract

The level of messenger ribonucleic acid specific for the argECBH gene cluster (arg-mRNA) of Escherichia coli was measured by deoxyribonucleic acid-ribonucleic acid hybridization in a number of strains. During the first 10 min after removal of arginine (derepression), the rate of arg-mRNA accumulation was six to ten times greater than that found in arginine-repressed argR(+) cells. In the absence of arginine, l-canavanine (200 mug/ml) repressed arg-mRNA synthesis to a level only 20 to 30% lower than that found after arginine deprivation. High levels of arg-mRNA were produced by argR(-) strains with or without added arginine. Within about 2 min after arginine addition to argR(+) cells, the rate of synthesis of arg-mRNA reached the repressed level. Likewise, 2.5 min after rifampin addition, all transcription of arg-mRNA was completed. These data are consistent with the view that arginine signals repression by inhibiting the initiation of transcription of arg-mRNA mediated in some way by the argR gene. The kinetics of arg-mRNA accumulation and the kinetics of completion of transcription together with the profile of hybridizable arg-mRNA in sucrose density gradients (major component 16S) suggest that the argECBH gene cluster is transcribed in short pieces rather than as a single unit.