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The yeast motor protein, Kar3p, is essential for meiosis I.

Bascom-Slack CA, Dawson DS - J. Cell Biol. (1997)

Bottom Line: The recognition and alignment of homologous chromosomes early in meiosis is essential for their subsequent segregation at anaphase I; however, the mechanism by which this occurs is unknown.We demonstrate here that, in the absence of the molecular motor, Kar3p, meiotic cells are blocked with prophase monopolar microtubule arrays and incomplete synaptonemal complex (SC) formation. kar3 mutants exhibit very low levels of heteroallelic recombination. kar3 mutants do produce double-strand breaks that act as initiation sites for meiotic recombination in yeast, but at levels severalfold reduced from wild-type.These data are consistent with a meiotic role for Kar3p in the events that culminate in synapsis of homologues.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.

ABSTRACT
The recognition and alignment of homologous chromosomes early in meiosis is essential for their subsequent segregation at anaphase I; however, the mechanism by which this occurs is unknown. We demonstrate here that, in the absence of the molecular motor, Kar3p, meiotic cells are blocked with prophase monopolar microtubule arrays and incomplete synaptonemal complex (SC) formation. kar3 mutants exhibit very low levels of heteroallelic recombination. kar3 mutants do produce double-strand breaks that act as initiation sites for meiotic recombination in yeast, but at levels severalfold reduced from wild-type. These data are consistent with a meiotic role for Kar3p in the events that culminate in synapsis of homologues.

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kar3 cells undergo interhomologue recombination at  severely reduced levels. Isogenic cultures of KAR3 (Dd519 +  MR820) and kar3 (Dd519) strains, heterozygous for a pair of arg4  heteroalleles (arg4RV and arg4Δ42), were induced to undergo  synchronous meiosis as described in Materials and Methods. Aliquots were removed at the indicated times and plated onto CM-Arg to determine the number of Arg+ recombinants. Aliquots  were also plated onto YPD or CM to determine total CFUs. Plotted is the ratio of Arg+ CFUs to total CFUs. There was little loss  of viability throughout the course of this experiment. The kar3  cells showed ∼5% of wild-type levels of recombination at 27 h.
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Figure 4: kar3 cells undergo interhomologue recombination at severely reduced levels. Isogenic cultures of KAR3 (Dd519 + MR820) and kar3 (Dd519) strains, heterozygous for a pair of arg4 heteroalleles (arg4RV and arg4Δ42), were induced to undergo synchronous meiosis as described in Materials and Methods. Aliquots were removed at the indicated times and plated onto CM-Arg to determine the number of Arg+ recombinants. Aliquots were also plated onto YPD or CM to determine total CFUs. Plotted is the ratio of Arg+ CFUs to total CFUs. There was little loss of viability throughout the course of this experiment. The kar3 cells showed ∼5% of wild-type levels of recombination at 27 h.

Mentions: Commitment of cells to meiotic levels of interhomologue recombination is a landmark event of meiosis that occurs in prophase I. To assay for interhomologue recombination, the frequency of prototroph formation at heteroallelic loci is measured at timed intervals in meiosis by returning meiotically-induced cells to vegetative growth (Sherman and Roman, 1963; Esposito and Esposito, 1974). Using a strain containing a pair of closely linked arg4 heteroallelic mutations, we were able to quantify the frequency of interchromosomal recombination events by selecting for Arg+ cells. The kar3 version of this strain was unable to commit to wild-type levels of heteroallelic recombination after 27 h, by which time the KAR3 control strain had reached maximal levels of recombination (Fig. 4). The mutant exhibited a gradual accumulation of Arg+ cells. By 27 h, the kar3 mutants showed ∼5% of wild-type levels of recombinants.


The yeast motor protein, Kar3p, is essential for meiosis I.

Bascom-Slack CA, Dawson DS - J. Cell Biol. (1997)

kar3 cells undergo interhomologue recombination at  severely reduced levels. Isogenic cultures of KAR3 (Dd519 +  MR820) and kar3 (Dd519) strains, heterozygous for a pair of arg4  heteroalleles (arg4RV and arg4Δ42), were induced to undergo  synchronous meiosis as described in Materials and Methods. Aliquots were removed at the indicated times and plated onto CM-Arg to determine the number of Arg+ recombinants. Aliquots  were also plated onto YPD or CM to determine total CFUs. Plotted is the ratio of Arg+ CFUs to total CFUs. There was little loss  of viability throughout the course of this experiment. The kar3  cells showed ∼5% of wild-type levels of recombination at 27 h.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2139793&req=5

Figure 4: kar3 cells undergo interhomologue recombination at severely reduced levels. Isogenic cultures of KAR3 (Dd519 + MR820) and kar3 (Dd519) strains, heterozygous for a pair of arg4 heteroalleles (arg4RV and arg4Δ42), were induced to undergo synchronous meiosis as described in Materials and Methods. Aliquots were removed at the indicated times and plated onto CM-Arg to determine the number of Arg+ recombinants. Aliquots were also plated onto YPD or CM to determine total CFUs. Plotted is the ratio of Arg+ CFUs to total CFUs. There was little loss of viability throughout the course of this experiment. The kar3 cells showed ∼5% of wild-type levels of recombination at 27 h.
Mentions: Commitment of cells to meiotic levels of interhomologue recombination is a landmark event of meiosis that occurs in prophase I. To assay for interhomologue recombination, the frequency of prototroph formation at heteroallelic loci is measured at timed intervals in meiosis by returning meiotically-induced cells to vegetative growth (Sherman and Roman, 1963; Esposito and Esposito, 1974). Using a strain containing a pair of closely linked arg4 heteroallelic mutations, we were able to quantify the frequency of interchromosomal recombination events by selecting for Arg+ cells. The kar3 version of this strain was unable to commit to wild-type levels of heteroallelic recombination after 27 h, by which time the KAR3 control strain had reached maximal levels of recombination (Fig. 4). The mutant exhibited a gradual accumulation of Arg+ cells. By 27 h, the kar3 mutants showed ∼5% of wild-type levels of recombinants.

Bottom Line: The recognition and alignment of homologous chromosomes early in meiosis is essential for their subsequent segregation at anaphase I; however, the mechanism by which this occurs is unknown.We demonstrate here that, in the absence of the molecular motor, Kar3p, meiotic cells are blocked with prophase monopolar microtubule arrays and incomplete synaptonemal complex (SC) formation. kar3 mutants exhibit very low levels of heteroallelic recombination. kar3 mutants do produce double-strand breaks that act as initiation sites for meiotic recombination in yeast, but at levels severalfold reduced from wild-type.These data are consistent with a meiotic role for Kar3p in the events that culminate in synapsis of homologues.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.

ABSTRACT
The recognition and alignment of homologous chromosomes early in meiosis is essential for their subsequent segregation at anaphase I; however, the mechanism by which this occurs is unknown. We demonstrate here that, in the absence of the molecular motor, Kar3p, meiotic cells are blocked with prophase monopolar microtubule arrays and incomplete synaptonemal complex (SC) formation. kar3 mutants exhibit very low levels of heteroallelic recombination. kar3 mutants do produce double-strand breaks that act as initiation sites for meiotic recombination in yeast, but at levels severalfold reduced from wild-type. These data are consistent with a meiotic role for Kar3p in the events that culminate in synapsis of homologues.

Show MeSH
Related in: MedlinePlus