Class I and class II ribonuclease H activities in Crithidia fasciculata (Protozoa).

The protozoan Crithidia fasciculata contains two different ribonuclease H activities. These enzymes display similar physical and biochemical characteristics to their homologues in higher eukaryotes, for instance calf thymus class I and class II ribonuclease H. Class I ribonuclease H of lower and higher eukaryotes can be activated by Mg2(+)- and Mn2(+)-ions. However, the presence of Mn2(+)-ions is inhibitory for the Mg2(+)-dependent class II ribonuclease H activity of Crithidia fasciculata and calf thymus. The protozoan class I-homologue enzyme appears to be serologically related to the class I ribonuclease H of calf thymus.     

水在不同条件下的相变和奇异相变

讨论了水在正常情况下的相变,并且利用液态低频力学谱方法对玻璃化转变研究领域中一个持续半个多世纪、十分令人困扰的热点水的玻璃化转变问题进行了研究.用表征玻璃化转变最直接的参量切变模量,首次实现了对水的玻璃化转变过程的明确表征,得出水的玻璃化转变温度是163K,而不是长期一直认为的136K.另外,水的玻璃化转变表现出不同于传统玻璃化转变的反常耗散行为.研究还表明,水的玻璃化转变温度表现出重要的同位素效应,这是水的玻璃化转变奇异特征的一个反映.     

Leishmania donovani in hamsters: stimulation of non-specific resistance by some novel glycopeptides and impact on therapeutic efficacy

Several glycopeptides structurally related to muramyl dipeptide (MDP) have been synthesized and evaluated for their ability to stimulate the non-specific resistance of hamsters against L. donovani infection. These compounds have been named CDRI compounds. The synthetic procedure used for compounds 86/448 and 84/212 is described. MDP and its synthetic congeners were administered as immunostimulants at a prophylactic dose of 3 mg/kg at two weeks interval. The challenge infection (1 x 10(7) amastigotes i.c./hamster) was given in between two doses of the compounds. One of the glycopeptides, CDRI comp. 86/448, has been found to be significantly more potent than MDP, effecting 92% inhibition of the challenge dose, whereas MDP produced only 26.5% inhibition. The effect of comp. 86/448 lasted until day 7 of challenge. The efficacy of sodium stibogluconate was appreciably improved in hamsters treated with comp. 86/448.     

A note on diagrams for turning-point diagnostics

A new diagram for discriminating a forecasting technique's history with respect to the two types of turning-point errors, missed turns and false signals is presented. This diagram extends Theil's original prediction-realization (P-R) presentation so that each of the four quadrants and the axes locates a distinct type of forecasting error or correct forecast, thus reducing much of the former ambiguity. This improvement is accomplished without the loss of any information.     

Geographic populations of the medfly may be differentiated by mitochondrial DNA variation

Restriction enzyme cleavage sites of mitochondrial DNA (mtDNA) from the Mediterranean fruit fly were found to vary among introduced populations in the Neotropics. The survey included samples from 15 established natural populations and 5 laboratory cultures from Hawaii, Central America, South America and West Africa and samples from recent California infestations (1989, 1991). Based on restriction fragment length polymorphisms from 2 enzymes, Hawaii is an unlikely source for the 1989 and 1991 California infestations. Interpopulational variation in mtDNA demonstrates the potential for the technique to trace the process of colonization (geographic spread) by this insect.     

Stimulation of polydnavirus replication by 20-hydroxyecdysone.

During oviposition the endoparasitic wasp Campoletis sonorensis, introduces a polydnavirus into parasitized insects where viral gene expression is required for endoparasite survival. The polydnavirus is integrated into wasp chromosomal DNA and replicates only in the ovary. Ecdysteroids regulate the developmental expression of many insect genes and may regulate polydnavirus replication. Direct verification of viral replication was performed by dot blot hybridization and by amplifying DNA sequences containing the viral integration site; this 'junction' fragment cannot be amplified from integrated virus. Thoracic ligations and in vitro ecdysteroid treatments of wasp ovaries support the hypothesis that polydnavirus DNA replication is regulated by ecdysteroid during parasite development.