FUNDAMENTAL AND APPLIED PERSPECTIVES IN RESEARCH OF THE VIRUS-LIKE PLASMIDS IN SACCHAROMYCES

Six types of the antagonistic activity (AA) in Saccharomyces were dist inguished and characterized. The K1, K2, K3 and K6 activities were ass ociated with the presence of the two kinds of cytoplasmic killer virus -like particles (VLP) - cytoplamic double-stranded RNAs (dsRNAs) consi sting of the main (L) and minor (M) species. All four antagonistic gro ups contained the L dsRNAs of the same size. The size of the M dsRNAs are dependent on the origin of the host strain. The cytoplasmic inheri tance of the K4 activity was observed among the strains which containe d no dsRNAs. The AA of this type was not connected with the integrity of mitochondria, also. The K5 activity was under chromosomal control. The optimum and the limits of pH for detection of the AA were dependen t on the type of activity. The natural route of extracellular infectio n by the killer VLPs was the penetration of the VLP into the early pro toplast-like spore sprouts. The variability of the K2 activity was stu died through mutagenesis of the marked genetic stocks. Twenty six chro mosomal genes were involved in the control of this activity. Most of t hese genetic determinants differed from the chromosomal determinants o f thc K1 activity in their phenotypes or localization. Four phenotypic ally different mutational defects of the M-2 plasmid affected thc mani festation of the K2 character. Epistatic and cumulative interactions b etween mutant chromosomal genes controlling the reproduction of the K2 plasmids were observed. Having compared the peculiarities of genetic control of the mutant phenotypes of the K1 and the K2 killers, we acqu ired the ability to propose a functional model of regulation of the ki ller virus-like plasmids reproduction. This model defines the interact ions between hypothetical gene products and killer dsRNAs or their int ermediates. The perspectives of selection of dsRNAs producers were stu died. The methods for construction and maintaining the productive stra ins from the diploids homozygous for a chromosomal mutation increasing the copy number of both K2 killer plasmids were developed. These meth ods assisted in obtaining the producers suitable for large-scale culti vation.