We investigated sex chromosome diversity in Zygosaccharomyces rouxii (Z. rouxii). In the current study, we show that the organization of the mating-type (MAT) locus is highly variable in the Z. rouxii population, indicating the MAT, HML, and HMR loci are translocation hotspots. Although NBRC1130 and CBS732 were originally two stocks of the type strain of the species, only NBRC1130 retains the original karyotype. A reciprocal translocation between the MAT and HMR loci appears to have occurred during the early passage culture of CBS732, which was used for genome sequencing. In NBRC1733, NBRC0686, NBRC0740 and NBRC1053, the terminal region of the chromosome containing the HMR locus was replaced with the chromosomal region to the left of the MAT or HML loci. The translocation events found in NBRC1733, NBRC0686, NBRC0740, and NBRC1053 were reconstructed under our experimental conditions using the DA2 background, and the reconstruction suggests that the frequency of this type of translocation is approximately 10−7. These results suggest that the MAT and MAT-like loci were the susceptible regions in the genome, and the diversity of mating-type chromosome structures in Z. rouxii was caused by ectopic exchanges between MAT-like loci.
The mechanism of whole-genome duplication (WGD) in yeast has been intensively studied because it has a large impact on yeast evolution. WGD has shaped the genomic architecture of modern ; however, the mechanism for restoring fertility after interspecies hybridization, which would be involved in the process of WGD, has not been thoroughly elucidated. In this study, we obtained a draft genome sequence of the salt-tolerant yeast NBRC110957 and revealed that it is a hybrid lineage of (allodiploid) with two subgenomes equivalent to NBRC1876. Because this allodiploid yeast can mate with other allodiploid strains and form spores, it can be a good model of restoring fertility after interspecies hybridization. We observed that NBRC110957 and NBRC1876 contain six mating-type-like () loci. There are no large deletions or deleterious mutations in loci, except for several-base-pair deletions in the X region in certain loci. We also assigned only one mating-type (MAT) locus that exclusively determines mating types from six loci. These results suggest that it is possible to recover mating competence regardless of whether cells lose one locus through random gene loss by mitotically dividing after interspecies hybridization. Moreover, we propose that perturbation of gene expression and substantial breakdown of heterozygosity caused by chromosomal rearrangement at loci play roles in restoring the mating competence of allodiploids. This scenario can provide a mechanism for restoring fertility after interspecies hybridization that is compatible with random gene loss models and suggests genomic plasticity during WGD in yeast. A whole-genome duplication occurred in an ancestor of the baker's yeast The origins of this complex and multifaceted process, which requires intra- or interspecies hybridization followed by dysfunction of one mating-type () locus to regain mating competence, has not been thoroughly elucidated. In this study, we provide a mechanism for regaining fertility in an interspecies hybrid, The draft genome sequence analysis and mating test showed that the strain used in this study is an intact interspecies hybrid, suggesting that it is possible to recover fertility regardless of whether cells lose one locus.
To characterize aspartyl aminopeptidase from Aspergillus oryzae, the recombinant enzyme was expressed in Escherichia coli. The enzyme cleaves N-terminal acidic amino acids. About 30% activity was retained in 20% NaCl. Digestion of defatted soybean by the enzyme resulted in an increase in the glutamic acid content, suggesting that the enzyme is potentially responsible for the release of glutamic acid in soy sauce mash.
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