|Budget Amount *help
¥6,800,000 (Direct Cost : ¥6,800,000)
Fiscal Year 1991 : ¥300,000 (Direct Cost : ¥300,000)
Fiscal Year 1990 : ¥2,400,000 (Direct Cost : ¥2,400,000)
Fiscal Year 1989 : ¥4,100,000 (Direct Cost : ¥4,100,000)
UV irradiation treatment of the asexual yeast Candida albicans, as well as C. tropicalis, gave rise to morphological mutants exhibiting abnormal colonies. The frequency of occurrence of these colony mutants was 10^<-2> to 10^<-3> and these phenomena were termed as genetic instability. Pulsed-field gel electrophoresis (PFGE) showed different banding pattern of chromosome-sized DNA, suggesting the occurrence of chromosonal rearrangements associated with genetic instability. These mutant strains produced cells of specific type to each type of colony. Furthermore, large cells with polyploid states were also found among these mutant colonies.
In order to clarify relation between the occurrence of polyploid cells and genetic instability, a variant of C. albicans strain, #31-30, was isolated, which produced polyploid cells when incubated at high temperature (37ﾟC). Incubation of this mutant stain at high temperature gave various morphological mutants and auxotrophic mutants at high frequency. These auxotrophic ones were produced as outaion previously existing heterozygous state to be homozygous oife. At low temperature (28ﾟC), scarecely any polyploid cells appeared, nor mutant colonies were produced. By protoplast fusion, this mutant phenotype was capable of being transferred to the other strains of C. albicans. with different genetic backgrounds.
Polyploid cells, which appeared after 37ﾟC-treatment, were fractionated by Ficoll-density gradient centrifugalization and plated to colonies. Among these colonies, auxotrophic ones as well as colony-morphology variants accounted for more than 20%. Hybridization experiments showed that some of the different patterns of chromosomal DNA bands among the mutant strains with genetic instability had RDNA repeats.
In the case of protoplast fusion, chromosome arramgement was found to occur during fusion process and two types of repeated sequences were detected, one of which was RDNA but the other remained to be identified.