Abstract
A temperature-sensitive mutant defective in DNA replication, tsFT5, has been isolated from the mouse mammary carcinoma cell line FM3A. DNA synthesis in tsFT5 cells at a restrictive temperature (39 degrees C) has been characterized in detail. Incorporation of [3H]thymidine decreased rapidly after an increase in temperature to 39 degrees C and the incorporation was less than 20% and 10% of the initial level after 4 and 8 h, respectively. Analysis by DNA fiber autoradiography revealed that the initiation of DNA replication at the origin of the replicons was impaired in tsFT5 cells but that the DNA chain elongation rate of the mutant cells did not decrease at the nonpermissive temperature. tsFT5 cells were confirmed to belong to the complementation group which includes ts85 cells arrested mainly in the G2 phase at the nonpermissive temperature. It has been observed that the amount of ubiquintin-conjugated histone H2A (uH2A) in ts85 cells decreases at the nonpermissive temperature (Marunouchi, T., Yasuda, H., Matsumoto, Y., and Yamada, M. (1980) Biochem. Biophys. Res. Commun. 95, 126-131). The amount of uH2A in tsFT5 cells also decreased rapidly at 39 degrees C. This decrease occurred at the same time as or slightly preceding to reduction in DNA synthesis, and the reappearance of uH2A was followed by the restoration of DNA synthesis after the temperature was reduced. A similar temporal relationship between decrease in the amount of uH2A and reduction in DNA synthesis was observed in ts85 cells cultured at 39 degrees C. However, the rates of the decrease of uH2A and of the reduction in DNA synthesis in ts85 cells were slower than those observed in tsFT5 cells. A comparison of the thermolability of purified ubiquitin-activating enzyme E1s revealed that the E1 from ts85 cells had a thermolability intermediate between those of the E1 from tsFT5 cells and of the wild-type cells. A reduction in the phosphorylation of histone H1 was observed in tsFT5 cells cultured at 39 degrees C, but the reduction occurred several hours after the decrease in uH2A and the reduction in DNA synthesis.
Highlights
From the Department of Physiological Chemistry, Faculty of Pharmaceutical Sciences, University of Tokyo, 7-3-1Hongo, Bunkyo-ku, Tokyo 113,Japan
It has been observed that theamount of ubiquitin- tantsthatare defective in DNA replication have greatly conjugated histone H2Ain ts86cells decreases contributed to the identification of replication enzymes and at the nonpermissive temperature
The rates of the decrease of uH2A and of the reduction in DNA synthesis in ts86 cells were slower many cell division cycle ts mutants have been isolated from Saccharomycecserevisiae and Schizosaccharomyces pombe and used for the identification and isolation of genes involved in the progression of the cell cycle [1,2]
Summary
RIKEN Gene Bank, Tukuba Life Science ResearchCenter, RIKENInstitute, 3-1-1Koyadai, Tukuba Science.
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