Yeast Cell Division Cycle Research Articles

Genetic control of the cell division cycle in yeast.

Genetic control of the cell division cycle in yeast.

Genetic control of the cell division cycle in yeast: IV. Genes controlling bud emergence and cytokinesis

Temperature-sensitive mutations in one gene ( cdc1) of Saccharomyces cerevisiae confer a defect in bud emergence. Asynchronous cultures of cells defective in cdc1 collect uniformly as unbudded cells (or cells with very tiny buds) following a shift from the permissive to the restrictive temperature. Studies with synchronous cultures demonstrate that the thermolabile product of cdc1 completes its function (the execution point) for bud emergence at the time of bud emergence (0.2 fractions of a cell cycle). When this function is not completed at the restrictive temperature. cells complete DNA replication but do not undergo nuclear division. Temperature-sensitive mutations in four genes ( cdc3, 10, 11, and 12) result in a defect in cytokinesis. At the restrictive temperature these mutant strains develop multiple elongated buds that do not separate from the parent cell. An assay for cytokinesis in yeast was developed and the mutants were shown not to have completed this process. The mutants undergo several rounds of DNA replication and nuclear division at the restrictive temperature and hence become multinucleate. The execution points for these gene products were determined in synchrony experiments to be at approx. 0.08 ( cdc11), 0.27 ( cdc3) and 0.58 ( cdc10) fractions of a cell cycle. Cytokinesis takes place at 0.9 fractions of a cell cycle. I conclude from these observations that bud emergence is not a necessary prerequisite for the completion of DNA replication but is apparently necessary for nuclear division. Cytokinesis and cell separation are not necessary prerequisites for bud emergence, DNA replication, or nuclear division.

Genetic control of the cell division cycle in yeast: III. Seven genes controlling nuclear division

Temperature-sensitive mutations in seven genes ( cdc 2, 6, 7, 9, 13, 14, and 15) of Saccharomyces cerevisiae confer a defect in nuclear division. Following a shift from the permissive to the restrictive temperature, asynchronous populations of these mutant cells accumulate uniformly in nuclear division. Depending upon the particular gene defect, mutants appear to terminate development at an early stage of nuclear division ( cdc 2), at a medial stage ( cdc 6, 7, 9, 13), or at a late stage ( cdc 14, 15). Experiments employing temperature shifts, time-lapse photomicroscopy, and synchronous cultures permitted a determination of the time in the cell cycle at which each of the thermolabile gene products completes its function at the permissive temperature (the execution point) for the ensuing nuclear division. These studies reveal a program of gene activity required for nuclear division that commences at the beginning of the cell cycle. Subsequent to the block in nuclear division the mutant strains do not undergo cell separation or bud initiation. Apparently, nuclear division is normally a prerequisite for the latter two processes.

Genetic control of the cell division cycle in yeast: II. Genes controlling DNA replication and its initiation

Temperature-sensitive mutations occurring in two unlinked complementation groups, cdc4 and cdc8, are recessive and result in a defect in DNA replication at the restrictive temperature. Results obtained with synchronous cultures suggest that cdc4 functions in the initiation of DNA replication and cdc8 functions in the propagation of DNA replication. From the behavior of mutant strains carrying lesions in cdc4, or in cdc8, or in both genes it is concluded that: (1) nuclear division and cell separation in yeast are dependent upon prior DNA replication; (2) a cellular clock controls bud initiation and the running of this clock is independent of the other events in the cycle, DNA replication, nuclear division and cell separation; (3) premature bud initiation is normally prevented as a consequence of the successful initiation of DNA replication.

Genetic control of the cell-division cycle in yeast. I. Detection of mutants.

Time-lapse photomicroscopy has been utilized to detect temperature-sensitive yeast mutants that are defective in gene functions needed at specific stages of the cell-division cycle. This technique provides two types of information about a mutant: the time at which the defective gene function is normally performed, defined as the execution point, and the stage at which cells collect when the function is not performed, defined as the termination point. Mutants carrying lesions in three genes that control the cell-division cycle are described. All three genes, cdc-1, cdc-2, and cdc-3, execute early in the cell cycle at about the time of bud initiation, but differ in their termination points. Cells carrying the cdc-1 mutation terminate at the execution point, most cells ending up with a tiny bud that does not develop further. Cells carrying the cdc-2 mutation terminate at mitosis. Cells carrying the cdc-3 mutation are defective in cell separation but show no definite termination point since other processes of the cell cycle, such as bud initiation and nuclear division, continue despite the block in cell separation.