The MATA locus of Yarrowia lipolytica, which was on the basis of its ability to induce sporulation in a diploid B/B strain, represses the mating capacity of this strain. The gene functions required for induction of sporulation and repression of conjugation could be separated by subcloning. Sequence analysis revealed two ORFs in the MATA locus. One of them (MATA1) codes for a protein of 119 amino acids which is required to induce sporulation. The other (MATA2) codes for a protein of 291 amino acids that is able to repress conjugation. Both genes are oriented divergently from a central promoter region, which possesses putative TATA and CAAT boxes for both genes. The product of MATA1 shows no homology to any known protein and seems to represent a new class of mating-type genes. MATA2 contains a HMG box with homology to other mating-type genes. Both MATA1 and MATA2 are mating-type specific. In cells of both mating types, the regions flanking the MATA locus contain sequences with homology to either S. cerevisiae SLA2 and ORF YBB9, respectively. From hybridization and subcloning data we estimate that the MATA region is approximately 2 kb long and is present only once in the genome.
During sporulation of diploids from crosses between different strains of the yeast Saccharomycopsis (Candida) lipolytica irregular numbers of ascospores per asciis have been observed. Using the serial section method it could be shown now by means of electron microscopy that in one-, two-, and three-spored asci unenclosed "naked" nuclei occur additionally to nuclei incorporated in mature spores. It was demonstrated that the production of less than four spores per ascus in this yeast is not the result of a lack of meiotic products but of the nonutilization of nuclei from meiosis. I n 2-4 spored asci usually four products of meiosis in form of enclosed and free nuclei could be demonstrated which indicate a normal meiotic division. All ascospores derived from asci with different spore numbers are uninuclear. It is assumed that a defect in spore formation caused by structural changes of chromosomes or aneuploidy should give rise to the occurrence of non incorporated nuclei and spore irregularity. It was concluded that meiosis and spore formation in Further works dealing with complementation, genetic recombination, conjugation, and sporulation opened the way to extensive and fundamental genetic studies of this yeast which is of special interest because of its ability to metabolize hydrocarbons and to convert this ubiquous material into single cell protein and other products Strains of Srn. Zipolytica isolated froin natural sources or strains from culture collections which recently have been shown t o possess a perfect state after crosses are known to form on sporulation niedium frequently asci with an irregular number of ascospores per ascus. The spores usually vary strongly in their shape and their fertility is very low, Genetic analysis and strain improvement is handicapped by these irregularities. Therefore, in certain laboratories attempts have been made to construct strains with whole tetrads and increased spore fertility for tetrad analysis. The background of spore irregularities in this yeast, however, remains open so far. The only explanation for abnormal spore forniation was given by ESSER and STAHL (1976) whch assumed on the base of light microscopic and genetical studies that the variability in the ascospore number is caused by the absence of a correlation between meiotic divisions and spore wall formation. This assumption differs strongly from the situation in Saccharomyces cerevisiae (BLACK and GORMAN 1971
In ultrathin sections and negatively stained isolates from protoplasts of a strain of Saccharomyces cerevisiae showing abnormal morphology and degeneration phenomena the presence of virus-like particles within the cells could be demonstrated. The isometric particles have diameters of about 50 nm, the electron dense centre is surrounded by distinct envelope. Protoplastic containing up to 30,000 particles could be found. It could be demonstrated that there exists a correlation between the amount of particles and the degree of degeneration of the cellular substructure. Protoplasts with high titres of virus-like particles obviously undergo lysis. Plaque formation on agar plates could not be seen. It is concluded that the phenomena observed can be compared with cytopathological effects caused by viruses in other cell systems.
During sporulation of diploids from crosses between different strains of the yeast Saccharomycopsis (Candida) lipolytica irregular numbers of ascospores per ascus have been observed. Using the serial section method it could be shown now by means of electron microscopy that in one-, two-, and three-spored asci unenclosed "naked" nuclei occur additionally to nuclei incorporated in mature spores. It was demonstrated that the production of less than four spores per ascus in this yeast is not the result of a lack of meiotic products but of the nonutilization of nuclei from meiosis. In 2--4 spored asci usually four products of meiosis in form of enclosed and free nuclei could be demonstrated which indicate a normal meiotic division. All ascospores derived from asci with different spore numbers are uninuclear. It is assumed that a defect in spore formation caused by structural changes of chromosomes or aneuploidy should give rise to the occurrence of non incorporated nuclei and spore irregularity. It was concluded that meiosis and spore formation in Saccharomycopsis lipolytica seem to represent parallel and coordinated processes which generally resemble those recorded for Saccharomyces cerevisiae and Hansenula species.
Actin distribution was examined during the cell cycle of the dimorphic yeast Yarrowia lipolytica, showing the correlation between bud growth, nuclear migration and rearrangement of the actin cytoskeleton. The results correspond with observations made in cells of Saccharomyces cerevisiae, S. uvarum and Candida albicans. Localization of actin was also determined in hyphal cells, where actin is stained predominantly in the tip and also at the septum of hyphae. The standard methods used for tubulin immunostaining in S. cerevisiae and C. albicans cells were adapted for application in Y. lipolytica. Copyright © 1999 John Wiley & Sons, Ltd.
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