Isolation and characterization of the TRM1 locus, a gene essential for the N2,N2-dimethylguanosine modification of both mitochondrial and cytoplasmic tRNA in Saccharomyces cerevisiae

The trm1 mutation of Saccharomyces cerevisiae is a single nuclear mutation that affects a specific base modification of both cytoplasmic and mitochondrial tRNA. Transfer RNA isolated from trm1 cells lacks the modified base N2,N2-dimethylguanosine, and extracts from these cells do not have detectable N2,N2-dimethylguanosine-specific tRNA methyltransferase activity. As part of our efforts to determine how this mutation affects enzyme activities in two different cellular compartments we have isolated the TRM1 locus by genetic complementation. The TRM1 locus restores the N2,N2-dimethylguanosine modification to both cytoplasmic and mitochondrial tRNA in trm1 cells. An open reading frame in this TRM1 gene is essential for complementation of the trm1 phenotype. Expression of this open reading frame in Escherichia coli converts the organism from one that neither makes N2,N2-dimethylguanosine nor has N2,N2-dimethylguanosine-specific tRNA methyltransferase activity into one that does. This result suggests that the TRM1 locus is the structural gene for the tRNA modification enzyme and that both nuclear/cytoplasmic and mitochondrial forms of the methyltransferase are produced from the same gene.     

Suicide vector for transposon mutagenesis in Pseudomonas solanacearum.

A suicide vector was constructed by cloning the transfer genes of the wide-host-range (IncW group) plasmid R388 into the BamHI site of pBR325. This plasmid can deliver Tn5 into Pseudomonas solanacearum at frequencies ranging from 10(-6) to 10(-9) per recipient.     

Succulence and CAM relationships in Aeonium genus

The CAM has been tested in six species of the Aeonium genus by studying the diurnal fluctuation of organic acids, pH and night fixation of CO₂. The existence of a mesophyll structure able to support this metabolism has been shown as well as a congruent periodicity in the pool of cell starch. We have calculated the S, ES and Sm indices in the six species. A series of regression equations of different grades and types were calculated and shown to have correlation coefficients statistically significant. This allows us to confirm the suitability of the Sm index as a rapid test to establish the CAM as postulated by former authors.     

Extracellular action potentials recorded from the interior of the giant esophageal cell of Ascaris

Exploration of the cytoplasm of the giant esophageal cell of Ascaris with a recording microelectrode shows the existence of shallow spaces where the microelectrode tip becomes extracellular in spite of being in the interior of the cell. When the microelectrode penetrates into these spaces from the cytoplasm, the resting potential shifts to a different level or entirely disappears. At the same time the large intracellular spikes are replaced by small transients similar to extracellularly recorded action potentials. It is concluded that such spaces are in communication with the external solution, and separated from the cytoplasm by an electrically active membrane; i.e., able to generate action potentials. Measurement of the potential differences between the interior of the spaces and the external solution shows that although some are not polarized, many spaces have a resting potential of the same polarity as that of the cytoplasm. It is suggested that although they are of larger size these spaces may be equivalent to the tubular systems which in other muscle cells are known to be involved in the spread of excitation into the cytoplasm.     

Influence of Some Ions on the Membrane Potential of Ascaris Muscle

The influence of several ions on the membrane potential of the somatic muscle of Ascaris has been investigated by changing their concentration in the surrounding solution. When [K]_o is increased at the expense of [Na]_o leaving [Cl]_o constant, the membrane potential is first seen to increase. [K]_o higher than 45 mM reduces the membrane potential with a slope of 23 mv for a tenfold change in [K]_o. However, when [K]_o is increased keeping [Na]_o and [Cl]_o low and constant, the line relating the membrane potential with log [K]_o has a slope of almost 50 mv. If [Cl]_o is reduced in the absence of external Na, after the [K]_o is increased to 45 mM, the membrane potential decreases with a slope of 59 mv per tenfold change in [Cl]_o in close agreement with the Nernst equation. If Cl^- is replaced by SO₄ ^2-, a depolarization is produced, while chloride replacement by NO₃ ^-, Br^-, and I^- results in a hyperpolarization of the membrane. Removal of the external Na⁺ ions increases the average membrane potential by 17 mv.     

白翅叶蝉Empoasca subrufa Melichar的研究

白翅叶蝉是福建省水稻的重要害虫,苗期受害严重者,整片稻苗苍白,甚至枯死;早稻孕穗、抽穗期常大量发生为害,影响谷粒饱满度,造成减产。福州和闽侯地区一年发生4代,部分5代。成虫越冬。冬季日平均温度达11℃以上时仍能取食为害。春季成虫侵入稻田,4月下旬前后大量产卵,5月中旬虫数激增,5月下旬或6月初达到高峰。早稻收割时由于农事活动引致若虫大量死亡。晚稻田于8、9月虫数较多,但危害不如早稻严重。10月中旬以后成虫逐渐离开稻田,迁往越冬场所。 寄主植物幼嫩茂密和较大湿度的小生境有利于白翅叶蝉的发育繁殖。大发生的气候因子主要是春季多雨。适宜的温湿度范围为温度20—25℃,相对湿度85—90%。 DDT单独使用或DDT与666混用防治白翅叶蝉都能收到满意的效果。早稻秧田宜在播种后两周施药防治;本田于5月中旬虫口密度开始增长之际施药,亦能抑制为害。冬季小麦出土以前清除田边杂草,也是一项有效的防治措施     

Acetylcholine sensitivity of the spine-test articular capsule of the sea urchin Eucidaris tribuloides

1. The changes in the consistence of the spine-test articular capsule, or ligament, of the primary spines of Eucidaris tribuloides induced by acetylcholine (ACh) have been studied. Two complementary techniques were used: (a) "forced-vibration", which detects variations in the stiffness of the ligament along a single diametral plane; and (b) "forced-rotation" which records the spatial distribution of those changes. 2. ACh (1 microM to 1 mM) caused a rapid increase in the resistive force opposed by the ligament to passive stretching. Similar effects were elicited by several monoquaternary, N-substituted derivatives of trimethylammonium. 3. The opposite effect, i.e. softening, was induced by decamethonium, dimethylphenylpiperazine, and 2-ketoamyltrimethylammonium. 4. The involvement in these effects of ACh-binding groups with pharmacological properties similar to those of the "anionic sites" of nicotinic ACh receptors is suggested.