Ribonuclease II Activity in a “Presumptive” Ribonuclease II-Deficient Mutant

A mutant strain of Escherichia coli previously thought to possess low levels of ribonuclease II activity has normal levels of ribonuclease II after partial purification of this enzyme from crude extracts.     

“整合物种概念”和“分化路上的物种”

已有的各个物种概念对物种的认识类似盲人摸象, 只包含了物种的某一个方面; 而一个分化后期的成熟物种应涵盖了所有的物种概念。但是, 尚未到达分化后期的物种往往又已开始新一轮的物种分化; 自然中存在的多数“物种”处于分化路上。这种循环往复连续分化产生的物种, 存在种间生殖隔离不彻底、基因流频繁发生、网状进化突出等现象。此外, 对于不同的物种对, 最早开始分化的基因以及不同物种概念所要求的条件的分化顺序不是统一的, 而是随机的。定义一个适合所有“分化路上的物种”概念存在较大困难。但是, 应采用尽可能多的物种概念来界定分化路上的物种、发表新种和进行分类处理; 也应承认种间可能广泛存在不完全的生殖隔离和有限的基因流, 即有不属于两个物种群体的杂交或回交个体的存在。这样划分的物种比只依据一个物种概念认定的物种具有更高的客观性和科学性。     

Specific Single or Double Proline Substitutions in the “Spring-loaded” Coiled-Coil Region of the Influenza Hemagglutinin Impair or Abolish Membrane Fusion Activity

We tested the role of the “spring-loaded” conformational change in the fusion mechanism of the influenza hemagglutinin (HA) by assessing the effects of 10 point mutants in the region of high coiled-coil propensity, HA2 54–81. The mutants included proline substitutions at HA2 55, 71, and 80, as well as a double proline substitution at residues 55 and 71. Mutants were expressed in COS or 293T cells and assayed for cell surface expression and structural features as well as for their ability to change conformation and induce fusion at low pH. We found the following: Specific mutations affected the precise carbohydrate structure and folding of the HA trimer. All of the mutants, however, formed trimers that could be expressed at the cell surface in a form that could be proteolytically cleaved from the precursor, HA0, to the fusion-permissive form, HA1-S-S-HA2. All mutants reacted with an antibody against the major antigenic site and bound red blood cells. Seven out of ten mutants displayed a wild-type (wt) or moderately elevated pH dependence for the conformational change. V55P displayed a substantial reduction (~60– 80%) in the initial rate of lipid mixing. The other single mutants displayed efficient fusion with the same pH dependence as wt-HA. The double proline mutant V55P/ S71P displayed no fusion activity despite being well expressed at the cell surface as a proteolytically cleaved trimer that could bind red blood cells and change conformation at low pH. The impairment in fusion for both V55P and V55P/S71P was at the level of outer leaflet lipid mixing. We interpret our results in support of the hypothesis that the spring-loaded conformational change is required for fusion. An alternate model is discussed.     

Sporulation of the “Thermophilic Anaerobes.”

A reasonable degree of synchrony in the sporulation of Clostridium thermosaccharolyticum 3814 was obtained by using three 10% transfers of 8-hr cultures in a medium containing 0.5% L-arabinose, 0.5% peptone, 0.5% yeast extract, and Gc minerals. Sporulation was stimulated by L-arabinose and L-xylose, but was repressed by glucose, mannose, fructose, and D-pentoses. Sporulating cells were long and thin, whereas repressed cells were shorter and thicker. The optimal pH for sporulation was in the range of pH 5.0 to 5.5. As sporulation continued, the accumulated acetate decreased. Label studies indicated that a significant amount of acetate-2-C¹⁴ was incorporated into the spore lipid. The calcium, phosphorus, and dipicolinic acid (DPA) concentrations on a dry weight basis were 2.55, 2.60, and 7.25%, respectively. The molar ratio of Ca-DPA was 1.47.     

Escherichia coli MazF Leads to the Simultaneous Selective Synthesis of Both “Death Proteins” and “Survival Proteins”

The Escherichia coli mazEF module is one of the most thoroughly studied toxin–antitoxin systems. mazF encodes a stable toxin, MazF, and mazE encodes a labile antitoxin, MazE, which prevents the lethal effect of MazF. MazF is an endoribonuclease that leads to the inhibition of protein synthesis by cleaving mRNAs at ACA sequences. Here, using 2D-gels, we show that in E. coli, although MazF induction leads to the inhibition of the synthesis of most proteins, the synthesis of an exclusive group of proteins, mostly smaller than about 20 kDa, is still permitted. We identified some of those small proteins by mass spectrometry. By deleting the genes encoding those proteins from the E. coli chromosome, we showed that they were required for the death of most of the cellular population. Under the same experimental conditions, which induce mazEF-mediated cell death, other such proteins were found to be required for the survival of a small sub-population of cells. Thus, MazF appears to be a regulator that induces downstream pathways leading to death of most of the population and the continued survival of a small sub-population, which will likely become the nucleus of a new population when growth conditions become less stressful.     

A “New” low incidence “Hutterite” blood group antigen waldner (Wda)

A “new” red cell antigen has been found so far only in members of Hutterite kindreds with the surname Waldner. The antigen, Wd^a, is inherited as an autosomal dominant and is not part of the ABO, Chido, Colton, Dombrock, Duffy, Kidd, MN, P, or Rh blood group systems.     

Antigenic Structure of Treponema pallidum, Nichols Strain II. Extraction of a Polysaccharide Antigen with “Strain-specific” Serological Activity

An ultracentrifugally homogeneous heat-stable polysaccharide preparation free from serologically reactive rabbit testicular tissue antigen, including cardiolipin, was extracted from the Nichols strain of Treponema pallidum, and found to react by complement-fixation with homologous rabbit sera but not with human syphilitic sera. In addition, the reactive "strain-specific" component was found to be distinct from a second reactive component within the preparation related to an antigen of T. reiteri.