Arginine auxotrophs of Candida albicans deficient in argininosuccinate lyase

Auxotrophic mutants of Candida albicans FC18 were induced by a combination of treatments with nitrous acid and UV irradiation. Arginine (Arg-), histidine (His-) and methionine/cysteine (MetA-) auxotrophs were recovered by this means. The Arg- auxotrophs lacked active argininosuccinate lyase (EC 4.3.2.1), the enzyme catalysing the final step in arginine biosynthesis. Thus the locus may be designated arg-4. The mutant strains bearing this mutation did not form germ tubes unless the germination medium contained arginine.     

Nonintegrative transformation in the filamentous fungus Podospora anserina: stabilization of a linear vector by the chromosomal ends of Tetrahymena thermophila.

The effect of the chromosomal ends of Tetrahymena thermophila on the stability of linear transforming molecules in the filamentous fungus Podospora anserina was tested. A derivative of an integrative vector for this fungus has been constructed, so that after linearization, the ends of the plasmid are the telomeric sequences of T. thermophila. After transformation, this linear molecule was maintained as an extrachromosomal plasmid with no integrated copies in about 50% of the transformants. Under selective conditions, there was approximately one linear molecule per 5 to 10 nuclei, and these extrachromosomal molecules were rapidly lost under nonselective conditions. The circular plasmid carrying an inverted repeat of T. thermophila telomeres could be linearized and processed in vivo.     

Influence of oxytocin on human memory processes: Validation by a control study

An earlier report (1) of an adverse effect of high doses of oxytocin on human memory included results of studies on women receiving oxytocin as part of the treatment to induce 2nd trimester therapeutic abortion. These women served as their own controls. We have now been able to study a group of women who have been treated in all ways like the original group, with the exception that they did not receive oxytocin. The results from this external control corroborate the finding that oxytocin affected memory.     

Cat satellite DNA. Isolation using netropsin with CsCl gradients

The absence of centromeric bands in the karyotype of Felis catus is confirmed. It is also confirmed that no satellite band is visible in CsCl density gradients. However, a satellite is observed both by recentrifuging the fraction of the DNA that bands at high density in CsCl and by using netropsin to enhance the resolution of a CsCl gradient containing total F. catus DNA. The satellite, about 0.5% of total DNA, was isolated by repeated centrifugation in CsCl alone and in CsCl with netropsin. Netropsin was removed and a pure satellite DNA obtained. The reassociation kinetics (C0t1/2 less than 10(-3) M . s) show that the satellite is of the simple sequence type and hence a candidate for centromeric heterochromatin. Its cytological localisation awaits in situ hybridisation experiments.     

Aggregation of tobacco mosaic virus by sodium chondroitin sulfate

The precipitation of tobacco mosaic virus by sodium chondroitin sulfate in an aqueous solution was investigated kinetically by means of turbidimetry. The virus solution became turbid after the addition of chondroitin sulfate. A threshold concentration of chondroitin, 1.33 mg/ml, was required for virus precipitation, irrespective of the virus concentration. The precipitation resulted from a mutual spatial exclusion phenomenon, leading to the separation of the virus as a crystalline phase. The dimension of chondroitin sulfate calculated at the threshold concentration agreed well with that obtained by other methods. The initial slopes and the aggregation half-times of the virus aggregates depended on both chondroitin and virus concentrations and the former increased with the increase in concentration of each. Above the threshold concentration of chondroitin sulfate, tobacco mosaic virus aggregation was a rapid-aggregation process and ended within 100 sec.     

Mechanism of action of ryanodine on cardiac sarcoplasmic reticulum

Ryanodine was found to initially inhibit calcium uptake by cardiac sarcoplasmic reticulum. This initial depression was followed by a later marked stimulation of calcium uptake. These effects were noted when calcium uptake was measured in the presence or absence of oxalate. The requirement for preincubation with ryanodine was highly dependent on ryanodine concentration and temperature. The mechanism of action of ryanodine clearly was not an effect on oxalate entry or calcium oxalate precipitation because the effects were also observed in the absence of oxalate. Ryanodine also had no effect on passive calcium efflux from actively loaded vesicles. Because ryanodine had no effect on Ca2+-ATPase activity under defined conditions of an ATP-regenerating system and no calcium gradient, we suggest ryanodine does not change the stoichiometry of the pump. Our results are consistent with the hypothesis that ryanodine closes a calcium channel in a subpopulation of the vesicles.