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Division Cycle of Myxococcus xanthus II. Kinetics of Stable and Unstable Ribonucleic Acid Synthesis¹

^a Department of Bacteriology and Institute of Molecular Biology, University of California, Los Angeles, California 90024

ABSTRACT

The kinetics of stable and unstable ribonucleic acid (RNA) synthesis during the division cycle of Myxococcus xanthus growing in a defined medium was determined. Under these conditions, M. xanthus contains one chromosome which is replicated during 80% of the cell cycle. Stable RNA synthesis was measured by pulselabeling an exponential-phase culture with radioactive uridine and then preparing the cells for quantitative autoradiography. By measuring the size of individual cells as well as the number of grains, the rate of stable RNA synthesis as a function of cell size was determined. Unstable RNA synthesis during the division cycle was determined by correlating the data for stable RNA synthesis with the relative amounts of stable and unstable RNA labeled during the short pulse. The data reported here demonstrate that: (i) cells synthesize both stable and unstable RNA throughout the division cycle; (ii) the rate of stable RNA synthesis increases in two discrete steps, corresponding to average ages of 0.15 and 0.75 generations; (iii) the rate of unstable RNA synthesis exhibits an initial rise, followed by a relatively constant rate of synthesis, and finally, a burst of unstable RNA synthesis prior to septum formation. The half-life of unstable RNA of M. xanthus, generation time of 390 min at 30 C, was 4 min. Comparison of the rates of stable and unstable RNA synthesis indicates noncoordinate RNA synthesis within the normal division cycle.

² Present address: Department of Biochemical Sciences, Moffett Laboratories, Princeton University, Princeton, N.J. 08540.

³ Present address: Microbiology Department, Tel Aviv University, Tel Aviv, Israel.

¹ A preliminary report of this study was presented at the 70th Annual Meeting of the American Society for Microbiology, Boston, Mass., 26 April-1 May 1970.

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