Advances in Biophysics最新文献

Among the genus Ipomoea, three morning glories, I. nil (the Japanese morning glory), I. purpurea (the common morning glory), and I. tricolor, were domesticated well for floricultural plants, and many spontaneous mutants displaying various flower pigmentation patterns were isolated. Most of these spontaneous mutations were found to be caused by the insertion of DNA transposable elements in the genes for the anthocyanin pigmentation in flowers, and many of them exhibited variegated flowers, such as white flowers with pigmented spots and sectors. Here, we describe the historical background of the mutants displaying variegated flowers and review the genetic and epigenetic regulation in flower pigmentation associated with transposable elements of these morning glories. The flecked, speckled, r-1, and purple mutations in I. nil were caused by insertions of Tpn1 and its relatives in the En/Spm superfamily, Tpn2, Tpn3, and Tpn4, into the genes for anthocyanin coloration in flowers, i.e., DFR-B, CHI, CHS-D, and InNHX1, respectively. Similarly, the flaked and pink mutants of I. purpurea have distantly related elements, Tip100 and Tip201, in the Ac/Ds superfamily inserted into the CHS-D and F3'H genes, respectively. The flower variegation patterns can be determined by the frequency and timing of the excision of these transposons, and their stable insertions produce plain color flowers without generating pigmented spots or sectors; furthermore, both genetic and epigenetic regulation appeared to play important roles in determining the frequency and timing of the excision of the transposons. However, flower variegation is not always associated with the excision of an integrated DNA transposon from one of the genes for anthocyanin pigmentation. The mutant Flying Saucers of I. tricolor displaying variegated flowers was found to have the transposon ItMULE1 inserted into the DFR-B promoter region, but no excision of ItMULE1 from the DFR-B could be detected in the variegated flower lines. The instable pearly-vrg allele in cv. Flying Saucers is likely to be an epiallele because the DNA methylation in the DFR-B promoter appeared to be associated with flower pigmentation.

Pairing between homologous DNA controls cellular functions including double-strand break repair, mitotic recombination, and progression of DNA replication forks, as well as chiasma formation during meiosis. Here I summarize that homologous interaction could promote the cell killing in bacteria, yeast, and multicellular organisms. The mechanisms of cell killing are categorized into two types: (1) the killing due to the accumulation of extrachromosomal DNA; (2) the killing induced by Holliday junction structures. I propose that the mechanisms of such killing function as novel apoptotic pathways in the cells carrying severe DNA damages to eliminate such damages from cell population.

The frequency of illegitimate recombination has been measured by a lambdabio transducing phage assay during the induction of the E. coli lambda c1857 lysogen. Illegitimate recombination falls into two classes, short homology-independent and short homology-dependent illegitimate recombination. The former involves sequences with virtually no homology, and is mediated by DNA topoisomerases and controlled by the DNA binding protein HU. The latter is induced by UV irradiation or other DNA damaging agents and requires short regions of homology, usually contain 4 to 13 base pairs, at sites involved in recombination. It has been shown that the RecJ exonuclease promotes short homology-dependent illegitimate recombination, but that the RecQ helicase suppresses it. In addition, we have shown that the overexpression of RecE and RecT enhances the frequencies of spontaneous and UV-induced illegitimate recombination and that the RecJ, RecF, RecO, and RecR functions are required for this RecE-mediated illegitimate recombination. Moreover, we have also indicated that RecQ plays a role in the suppression of RecEmediated illegitimate recombination, with the participation of DnaB, Fis, Exol, and H-NS. Models have been proposed for these modes of recombination: the DNA gyrase subunit exchange model for short homology-independent illegitimate recombination and the "double-strand break and join" model for short homologydependent illegitimate recombination. Many features of these models remain to be tested in future studies.