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 μg/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 16 S ) suggest that the argECBH gene cluster is transcribed in short pieces rather than as a single unit.