Mitochondrially-encoded protein Var1 promotes loss of respiratory function in Saccharomyces cerevisiae under stressful conditions

Stressed Saccharomyces cerevisiae cells easily lose respiratory function due to deletions in mitochondrial DNA, and this increases their general stress resistance. Is the loss active? We found that erythromycin (an inhibitor of mitochondrial translation) prevents the loss in control cells but not in the ones expressing mitochondrially-encoded protein Var1 in the nucleus. Var1 is a component of mitochondrial ribosomes; it is hydrophilic, positively charged, and prone to aggregation. Addition of DNase altered Var1 content in a preparation of mitochondrial nucleoids. Our data indicate that Var1 physically interacts with mitochondrial DNA and under stress negatively regulates its maintenance.     

General scheme of the phosphotriester condensation in the oligodeoxyribonucleotide synthesis with arylsulfonyl chlorides and arylsulfonyl azolides

Phosphotriester condensation (RO)(R'O)PO-2 (PDE) + R"OH (RO)(R'O)(R"O)PO (PTE) in the presence of arylsulfonyl chloride (ArSO2Cl) as well as arylsulfonyl azolides proceeds in two steps as revealed by 31P NMR spectroscopy. Pyrophosphotetraester (PPTE) accumulates in over 80% yield in the first step and converts to PTE in the second one. Nucleophilic catalysts of pyridine type (Nu1) are necessary in the first step. The second step is catalyzed by Nu1 as well as by catalysts of the tetrazole type (Nu2H). Base catalysis operates in the latter case. With Nu1 catalysts (pyridine, 4-N,N-dimethylaminopyridine, N-methylimidazole) the general scheme may be presented as follows: ArSO2Cl + Nu1 in equilibrium ArSO2Nu+1 + Cl-; ArSO2Nu+1 + PDE----(RO)(R'O)P(O)OSO2Ar (I); I + Nu+1----(RO)(R'O)P(O)Nu+1 (II); II + PDE in equilibrium [(RO)(R'O)PO]20; II + R"OH----(RO)(R'O)(R"O)PO. Catalysts of Nu2H type don't accelerate PPTE formation. In the second step they participate most probably in the process PPTE + Nu2H in equilibrium (RO)(R'O)P(O)Nu2 (III) + PDE; III + R"OH----(RO)(R'O)(R"O)PO + H+. The latter step is subjected to strong base catalysis.     

A novel approach to nonradioactive hybridization assay of nucleic acids using stained latex particles.

The paper describes a sensitive latex hybridization assay (LHA) method applied for indirect detection of biotinylated nucleic acid hybrids immobilized on a synthetic membrane. The biotinylated hybrids were visualized by means of latex particles containing the fluorescent dye pyronine G and coated with streptavidin; 1.6 and 0.3 pg of lambda-phage DNA was detected by dot blot hybridizations on nylon membrane and polyethyleneimine-cellophane, respectively. The assay sensitivity was increased by three orders of magnitude over that with fluorescently labeled probes due to encapsulation of the fluorescent dye in polymer particles. LHA is simple (single-stage detection procedure), fast, and more sensitive than any of the other nonradioactive hybridization methods.     

Efficiency of the cyclic batch antibiotic fermentation

For a simple mathematical model of microbial product formation, the productivities of stationary and nonstationary cultivation methods (chemostat and cyclic batch) are compared. Conditions of superiority of the cyclic batch cultivation are characterized. The model includes substrate inhibition of the product formation and the age-dependent loss of productivity of the culture.