ABSTRACT
Circular chromosomes have frequently been observed in tumors of mesenchymal origin. In the fission yeast Schizosaccharomyces pombe, deletion of pot1+ results in rapid telomere loss, and the resulting survivors have circular chromosomes. Fission yeast has 2 bromodomain and extra-terminal (BET) proteins, Bdf1 and Bdf2; both are required for maintaining acetylated histones. Here, we found that bdf2, but not bdf1, was synthetically lethal with pot1. We also obtained a temperature-sensitive bdf2-ts mutant, which can grow at high temperatures but becomes camptothecin sensitive. This suggests that Bdf2 is defective at high temperatures. The cell cycle of the pot1 bdf2-ts mutant was delayed in the G2 and/or M phase at a semipermissive temperature. Furthermore, a temperature-sensitive mutant of mst1, which encodes histone acetyltransferase, showed a synthetic growth defect with a pot1 disruptant at a semipermissive temperature. Our results suggest that Bdf2 and Mst1 are required for the growth of cells with circular chromosomes.
Subject(s)
SchizosaccharomycesABSTRACT
The UV protection and singlet oxygen quenching of aloesaponarin I have been studied by means of laser spectroscopy. The excited-state intramolecular proton transfer that provides the UV protection takes place along only one of the molecule's two intramolecular hydrogen bonds, and this can be understood by considering the nodal pattern of the wave function. The functional groups participating in the excited-state intramolecular proton transfer also play important roles in the singlet oxygen quenching. Aloesaponarin I has a quenching rate constant larger than that of vitamin E and has a long duration of action due to its resistance to UV degradation and chemical attacks by singlet oxygen and free radicals.