RESUMEN
In mutants chl2, chl3, chl5, and chl6, which control mitotic chromosome transmission, the behaviour of the centromeric plasmids with various genes was analyzed. The main cause of chromosome instability in chl2, chl5, and chl6 is chromosome loss during cell division (1:0 segregation). The main cause of chromosome instability in chl3. is nondisjunction (2:0 segregation). According to this, the chl3 mutant, but not other chl's, cannot maintain the mini-chromosome with SUP11 gene. This gene causes cell death in high copy number. Chromosome nondisjunction in chl3 is also confirmed by the data on the mini-chromosome carrying CUP1 gene responsible for copper-resistance in yeast. The copper resistancy level in chl3 transformants is much higher than in chl5 or wild type transformants. Elevated copper resistance of chl3 transformants is caused by the transit accumulation of CUP1-carrying mini-chromosome in part of the cell population as a result of segregation mistakes upon cell divisions. Thus, the CHL3 gene is a new gene that controls the process of mitotic chromosome disjunction in yeast.
Asunto(s)
Deleción Cromosómica , Genes Fúngicos , Mutación , Saccharomyces cerevisiae/genética , Cromosomas Fúngicos , Marcadores Genéticos , Plásmidos , Ploidias , Transformación GenéticaRESUMEN
Hybrid yeast plasmids were constructed, containing the centromere loci CEN3 under the control of two inducible yeast promoters--GAL10 and PHO5. It was shown, that during the induction of transcription from the GAL10 promoter the decrease in mitotic stability of minichromosome is affected both by partial disruption of centromere function by transcription and by influence of galactose on the number of residual cell divisions. In two strains the activity of GAL10 promoter was considerably higher than that of the PHO5 promoter. It is proposed to use the effect of minichromosome destabilization for evaluation of the relative promoter strength.
Asunto(s)
Centrómero , Cromosomas , ADN de Hongos/genética , Plásmidos , Saccharomyces/genética , Transcripción Genética , Regiones Promotoras GenéticasRESUMEN
Mutants with high instability of chromosome III designated Chl+ (chromosome loss) were obtained after irradiation with UV the Z4221-3c1 haploid disomic for chromosome III. The Chl+ mutants can be divided into two classes: 1) CL2, CL3, CL7, CL9, CL11, CL12, CL13 with elevated level of spontaneous inter- and intragenic recombination; 2) CL4, CL8 which unstable maintenance of chromosome III not accompanied with elevation of mitotic recombination frequency. The CL4 and CL8 mutants also reveal, in contrast to other mutants, unstable maintenance of artificial mini-chromosomes with chromosomal replicator ARS1 and centromeric loci CEN3, CEN4, CEN5, CEN6, CEN11. Substitution of ARS1 for other yeast replicators (ARS2, ARS of 2 micron plasmid) leads to no stabilization of mini-chromosomes in mutants. The noncentromeric plasmids containing homologous replicator (or replicators) from Candida maltosa are maintained with the same frequency both in wild type and in mutants. So, the stability of mini-chromosomes in CL4 and CL8 is not connected with uneffective replication of these chromosomes. Instability of chromosome III and mini-chromosomes in CL4 and CL8 is controlled by two nonallelic genes designated chl14 and chl18. We suppose that these genes control the process of centromere interaction with mitotic spindle microtubules.
Asunto(s)
Cromosomas/ultraestructura , Saccharomyces cerevisiae/genética , Cromosomas/efectos de la radiación , ADN de Hongos/genética , ADN de Hongos/efectos de la radiación , Mitosis/efectos de la radiación , Mutación , Plásmidos/efectos de la radiación , Saccharomyces cerevisiae/efectos de la radiación , Transformación Genética/efectos de la radiación , Rayos UltravioletaRESUMEN
CL mutants with high instability of chromosome III were UV-induced in haploid strain disomic for chromosome III. The obtained CL mutants can be divided into two groups: (1) CL2, CL3, CL7, CL11-CL13 with elevated level of spontaneous inter- and intragenic recombination and (2) CL4, CL8 in which instability of chromosome III is not accompanied by elevation of mitotic recombination frequency. CL4 and CL8 mutants also show unstable maintenance of artificial minichromosomes with different chromosomal replicators and centromeric loci. The instability of chromosome III and minichromosomes in CL4 and CL8 is determined by two nonallelic genes designated ch14 and ch18. The role of ch14 and ch18 genes in mitotic chromosome transmission is discussed.