散斑壳属两近似种的表型性状和ITS序列分析比较研究

对针叶树散斑壳Lophodermium conigenum与其近似种南方散斑壳L.australe的形态学特征及生态习性等进行了比较研究,同时对这两个种8个菌株的rDNA-ITS区进行了PCR扩增和序列测定,结合GenBank中16个相关ITS序列构建了系统发育树。结果表明,L.conigenum与L.australe有着非常密切的关系。L.conigenum除子囊果形状、子座基部层、线纹和寄生性外,其余特征与L.australe基本相同。L.conigenum的ITS序列的G+C含量(51.0%)小于L.australe的G+C含量(54.0%)。在系统发育树中,此二种形成两个明显独立的分支,支持了依据形态学等表型性状的分类。二者种间及种内的遗传差异与寄主有较大的相关性,而与产地无明显关联。通过表型性状和ITS序列的分析与比较,可准确地将L.conigenum与L.australe鉴别开来。     

A single tryptic fragment of colicin E1 can form an ion channel: stoichiometry confirms kinetics.

The molecularity of the ion channel formed by peptide fragments of colicin has taken on particular significance since the length of the active peptide has been shown to be less than 90 amino acids and the lumen size at least 8 A. Cell survival experiments show that killing by colicin obeys single-hit statistics, and ion leakage rates from phospholipid vesicles are first order in colicin concentration. However, interpretation in molecular terms is generally complicated by the requirement of large numbers of colicin molecules per cell or vesicle. We have measured the discharge of potential across membranes of small phospholipid vesicles by following the changes in binding of potential sensitive spin labeled phosphonium ions as a function of the number of colicin fragments added. Because of the sensitivity of the method, it was possible to reliably investigate the effect of colicin in a range where there was no more than 0.2 colicins per vesicle. The quantitative results of these experiments yield a direct molecular stoichiometry and demonstrate that one C-terminal fragment of the colicin molecule per one vesicle is sufficient to induce a rapid ion flux in these vesicles. In addition, the experiments confirm earlier findings that the colicin fragments do not migrate from one vesicle to another at pH 4.5. Similar results are obtained with large unilamellar vesicles.