Produtividade de cultivares de arroz irrigado em função da época de semeadura.

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Determinação dos graus-dia e do número de dias para atingir o estádio de diferenciação da panícula de cultivares de arroz irrigado.

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DNA supercoiling inhibits DNA knotting

Despite the fact that in living cells DNA molecules are long and highly crowded, they are rarely knotted. DNA knotting interferes with the normal functioning of the DNA and, therefore, molecular mechanisms evolved that maintain the knotting and catenation level below that which would be achieved if the DNA segments could pass randomly through each other. Biochemical experiments with torsionally relaxed DNA demonstrated earlier that type II DNA topoisomerases that permit inter- and intramolecular passages between segments of DNA molecules use the energy of ATP hydrolysis to select passages that lead to unknotting rather than to the formation of knots. Using numerical simulations, we identify here another mechanism by which topoisomerases can keep the knotting level low. We observe that DNA supercoiling, such as found in bacterial cells, creates a situation where intramolecular passages leading to knotting are opposed by the free-energy change connected to transitions from unknotted to knotted circular DNA molecules

Soma térmica e número de dias para atingir os principais estádios de desenvolvimento de 16 cultivares de arroz irrigado.

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