Effect of Calcium Ions on Synthesis of T5-Specific Ribonucleic Acid

The arrest in the development of bacteriophage T5 and in the synthesis of phage-specific proteins in Escherichia coli F cells infected at a low calcium ion concentration (10-4 m) has been traced to a deficiency in the system for synthesis of a specific class of viral RNA. Previous studies have recognized that during an infection under standard conditions at 10-3 m Ca++ three classes of RNA are formed in sequence during the infective cycle. They are Class I RNA, which appears between 0 and 4 min after infection, and Class II and Class III RNA, commencing at 4 and 9 min, respectively. The predominant RNA species formed during the first 4 min of infection at 10-4 m Ca++ appears to be identical with that synthesized immediately after infection of cells at 10-3 m Ca++ and is therefore Class I RNA. By this time, however, the rate of RNA synthesis has fallen rapidly and thereafter there is a marked change in the composition of the RNA species. At 20 min after infection 75% of the product is Class II RNA. Upon elevation of the Ca++ concentration to 10-3 m the rate of RNA synthesis increases markedly. Class II RNA at greatly elevated levels is the immediate product, and 5 to 6 min later Class III is formed. The arrest in RNA synthesis at 10-4 m Ca++ does not result from the failure of the T5 DNA to inject completely into the host cell nor from a loss of the metabolic capacity of cells to generate nucleoside triphosphates and maintain them within the cell. The interruption in viral development at low calcium ion concentrations probably represents a malfunction of the machinery for DNA transcription beginning with the synthesis of Class II RNA. The cessation of Class I RNA synthesis at either high or low Ca++ concentration probably results from the action of a protein formed early in the infective cycle.