Evidence for the Presence of Inhibitors of Mitotic Factors during G1Period in Mammalian Cells

Our earlier studies indicated that the mitotic factors, which induce germinal vesicle breakdown and chromosome condensation when injected into fully grown Xenopus oocytes, are preferentially associated with metaphase chromosomes and that they bind to chromatin as soon as they are synthesized during...

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Bibliographic Details
Published in:The Journal of cell biology 1983-12, Vol.97 (6), p.1707-1713
Main Authors: Adlakha, Ramesh C., Sahasrabuddhe, Chintaman G., Wright, David A., Rao, Potu N.
Format: Article
Language:English
Subjects:
Cell cycle
Cell extracts
Cell fusion
Cells
Chromosomes
Condensation
HeLa cells
Interphase
Mitosis
Oocytes
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Summary:Our earlier studies indicated that the mitotic factors, which induce germinal vesicle breakdown and chromosome condensation when injected into fully grown Xenopus oocytes, are preferentially associated with metaphase chromosomes and that they bind to chromatin as soon as they are synthesized during the G2phase. In this study, we attempted to determine the fate of these factors as the cell completes mitosis and enters G1. Extracts from HeLa cells at different points during G1, S, and G2periods were mixed with mitotic extracts in various proportions, incubated, and then injected into Xenopus oocytes to determine their maturation-promoting activity. The maturation-promoting activity of the mitotic extracts was neutralized by extracts of G1cells during all stages of G1but not by those of late S and G2phase cells. Extracts of quiescent ( G0) human diploid fibroblasts exhibited very little inhibitory activity. However, UV irradiation of G0cells, which is known to cause decondensation of chromatin, significantly enhanced the inhibitory activity of extracts of these cells. These factors are termed inhibitors of mitotic factors (IMF). They seem to be activated, rather than newly synthesized, as the cell enters telophase when chromosomes begin to decondense. The IMF are nondialyzable, nonhistone proteins with a molecular weight of >12,000. Since mitotic factors are known to induce chromosome condensation, it is possible that IMF, which are antagonistic to mitotic factors, may serve the reverse function of the mitotic factors, i.e., regulation of chromosome decondensation.
ISSN:0021-9525