J. Biol. Chem., Vol. 265, Issue 1, 26-33, Jan, 1990
Isolation of temperature-sensitive cell cycle mutants from mouse FM3A cells. Characterization of mutants with special reference to DNA replication
T Eki, T Enomoto, A Miyajima, H Miyazawa, Y Murakami, F Hanaoka, M Yamada and M Ui
Department of Physiological Chemistry, Faculty of Pharmaceutical Sciences, University of Tokyo, Japan.
A large number of mutants that are temperature sensitive (ts) for growth
have been isolated from mouse mammary carcinoma FM3A cells by an improved
selection method consisting of cell synchronization and short exposures to
restrictive temperature. The improved method increased the efficiency of
isolating DNA ts mutants, which showed a rapid decrease in DNA-synthesizing
ability after temperature shift-up. Sixteen mutants isolated by this and
other methods were selected for this study. Flow microfluorometric analysis
of these mutants cultured at a nonpermissive temperature (39 degrees C) for
16 h indicated that five clones were arrested in the G1 to S phase of the
cell cycle, six clones were in the S to G2 phase, and two clones were
arrested in the G2 phase. The remaining three clones exhibited 8C DNA
content after incubation at 39 degrees C for 28 h, indicating defects in
mitosis or cytokinesis. These mutants were classified into 11
complementation groups. All the mutants except for those arrested in the G2
phase and those exhibiting defects in mitosis or cytokinesis showed a rapid
decrease in DNA synthesis after temperature shift-up without a decrease in
RNA and protein synthesis. The polyomavirus DNA cell-free replication
system, which consists of polyomavirus large tumor antigen and mouse cell
extracts, was used for further characterization of these DNA ts mutants.
Among these ts mutants, only the tsFT20 strain, which contains heat-labile
DNA polymerase alpha, was unable to support the polyomavirus DNA
replication. Analysis by DNA fiber autoradiography revealed that DNA chain
elongation rates of these DNA ts mutants were not changed and that the
initiation of DNA replication at the origin of replicons was impaired in
the mutant cells.