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Genome haploidization involves sequential loss of cohesin from chromosome arms and centromeres during two meiotic divisions. At centromeres, cohesin's Rec8 subunit is protected from separase cleavage at meiosis I and then deprotected to allow its cleavage at meiosis II. Protection of centromeric cohesin by shugoshin-PP2A seems evolutionarily conserved. However, deprotection has been proposed to rely on spindle forces separating the Rec8 protector from cohesin at metaphase II in mammalian oocytes and on APC/ C-dependent destruction of the protector at anaphase II in yeast. Here, we have activated APC/C in the absence of sister kinetochore biorientation at meiosis II in yeast and mouse oocytes, and find that bipolar spindle forces are dispensable for sister centromere separation in both systems. Furthermore, we show that at least in yeast, protection of Rec8 by shugoshin and inhibition of separase by securin are both required for the stability of centromeric cohesin at metaphase II. Our data imply that related mechanisms preserve the integrity of dyad chromosomes during the short metaphase II of yeast and the prolonged metaphase II arrest of mammalian oocytes.

Riboflavin or vitamin B2 is a water-soluble vitamin and a precursor of flavin coenzymes, flavin mononucleotide, and flavin adenine dinucleotide, which play a key role as enzyme cofactors in energy metabolism. Candida famata yeast is a promising producer of riboflavin, as it belongs to the group of so-called flavinogenic yeasts, capable of riboflavin oversynthesis under conditions of iron starvation. The role of the particular structural genes in the limitation of riboflavin oversynthesis is not known. To study the impact of overexpression of the structural genes of riboflavin synthesis on riboflavin production, a set of plasmids containing genes RIB1, RIB6, and RIB7 in different combinations was constructed. The transformants of the wild-type strain of C. famata, as well as riboflavin overproducer, were obtained, and the synthesis of riboflavin was studied. It was found that overexpression of RIB1 and RIB6 genes coding for enzymes GTP cyclohydrolase II and 3,4-dihydroxy-2-butanone-4-phosphate synthase, which catalase the initial steps of riboflavin synthesis, elevated riboflavin production by 13–28% relative to the parental riboflavin-overproducing strains.

Riboflavin or vitamin B 2 is an essential dietary component for humans and animals that is the precursor of flavin coenzymes flavin mononucleotide and flavin adenine dinucleotide involved in numerous enzymatic reactions. The flavinogenic yeast Candida famata overproduces riboflavin under iron starvation; however, regulation of this process is poorly understood. Regulatory gene SEF1 encoding transcription activator has been identified. Its deletion blocks yeast ability to overproduce riboflavin under iron starvation. It was shown here that the SEF1 promoters from other flavinogenic (Candida albicans) and non-flavinogenic (Candida tropicalis) yeasts fused with the open reading frame (ORF) of SEF1 gene from C. famata are able to restore riboflavin oversynthesis in sef1Δ mutants. It is known that in the pathogenic flavinogenic yeast C. albicans, Sfu1 (GATA-type transcription factor) represses SEF1. Here, we found that deletion of SFU1 gene in wild-type C. famata leads to riboflavin oversynthesis. Moreover, it was shown that disruption of VMA1 gene (coding for vacuolar ATPase subunit A) also results in riboflavin oversynthesis in C. famata.

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