Synthesis of early phage messengers in Escherichia coli infected by T4 during a specific amino acid deficiency

Abstract

It has been known for many years that the rate of ribosomal and transfer RNAs synthesis in bacteria is determined by the internal amino acid concentration but the existence of the same mechanism of regulation for messenger RNA has not been clearly demonstrated yet.This work was done to determine if the amino acid regulation also governs phage early messenger RNA synthesis in T4 infected Escherichia coli cells, in which the synthesis of bacterial RNA is known to be turned off rapidly after infection.The determination of the rate of messenger synthesis in the presence and in the absence of the required amino acid was done (a) by measurement of the amount of radioactivity from labelled RNA which is hybridizable to phage DNA; (b) by estimation in each sample of the amount of messenger RNA which can compete with a messenger RNA labelled in the presence or in the absence of the required amino acid for the complementary sites of phage DNA.By direct hybridization it was found that in the absence of the required amino acid the rate of labelling of phage messenger RNA is reduced in a stringent strain, but not in a relaxed strain.By hybridization competition it was found that the molecular species of phage messenger RNA which can be synthesized in the absence of the required amino acid are present at the same concentration in infected cells either in the presence or in the absence of the amino acid.A study of the kinetics of formation of the messenger pool showed that, as early as the first minute of infection, all the molecular species of messenger are present in the same proportions in the stringent cells whether amino acid‐starved or not.It is concluded that in a stringent strain those molecular species of messenger which do not require the presence of specific viral protein for their formation are synthesized at the same rate in the presence or in the absence of a required amino acid.The implications of these results concerning the control of transcription by amino acids are discussed.