Deoxyribonucleotide biosynthesis in yeast: assay and properties of ribonucleotide reductase in permeabilized Saccharomyces cerevisiae cells

Yeast cells permeabilized by freeze-thaw cycles in a sorbitol-containing medium provide an experimentally favorable system for the study of ribonucleotide reduction in a small number of cells or in mutant strains. Ribonucleotide reductase activities determined in such cells are about twice those found in cell extracts but properties of the enzyme, except pH optimum, are closely comparable in both assay procedures. In contrast with other organisms, the activities measured in permeabilized cells from both diploid or haploid strains exceed the demand for deoxyribonucleotide formation during replication of the yeast genome. The method has been applied to yeast cultures growing in the presence of the ribonucleotide reductase inhibitor hydroxyurea and a twofold increase of enzyme activity has been established in such cells. On the other hand, analysis of a series of hus mutants, selected for hydroxyurea sensitivity in the laboratory of Singer and Johnston did not reveal obvious alterations of the enzyme vs the parental strains, suggesting that the hus phenotype may be due to lesions other than in ribonucleotide reductase.     

Propagation of individual spikes as "patches" of activation in isolated feline duodenum

Asynchrony of spikes has made it difficult to study the spatial and temporal behavior of spikes in the gastrointestinal system. By simultaneously recording from a large number of closely spaced electrodes, we investigated the propagation of individual spikes. Recordings were performed from the serosal surface of the isolated feline duodenum at 240 sites simultaneously. Analysis of the tracings made it possible to reconstruct the propagation of individual spikes. Spikes propagate in the longitudinal and circumferential directions in self-limiting areas or "patches." Conduction within patches may occur in the orad or aborad direction irrespective of the direction of the slow wave. Most of the patches are smaller (<40 mm(2)), although inhomogeneous activation by the preceding slow wave may increase their size. Stimulation by ACh, TTX, or tetraethylammonium does not affect the average patch size but does increase significantly their number and distribution in the duodenum [from 26% (control) to 56%, 61%, and 72%, respectively]. In conclusion, individual spikes activate limited areas or patches in the small intestine, and pharmacological stimulation increases the number and distribution of these patches. In the small intestine, this pattern of activation would induce localized contractions. Contraction could be modulated by the size, number, and distribution of spike patches.     

Acoustic divergence between bottlenose dolphin whistles from the Central–Eastern North Atlantic and Mediterranean Sea

To improve our understanding of the complex genetic and ecological structure of bottlenose dolphin (Tursiops truncatus) populations, we examined the acoustic features of communication signals from two geographically contiguous areas: the Central–Eastern North Atlantic and the Mediterranean Sea. Variations in the whistles were evaluated for four locations. Ten signal parameters were measured and used to statistically differentiate between the areas. Over 79 % of sightings were correctly classified by discriminant function analysis, confirming an acoustic differentiation between the two basins. The results of cluster analysis using the mean values of the parameters for each sighting showed that the three easternmost sightings from the Mediterranean and one sighting from the Canary archipelago formed a separate cluster from the rest of the Atlantic. The two sightings from the Alboran Sea in the west Mediterranean were grouped with the Atlantic recordings. There was more variability in whistles from the Atlantic Ocean consistent with data from genetic and photo-identification studies that document resident and non-resident animals in the area. The results suggest that the Alboran area may be inhabited by animals differentiated from the rest of the Mediterranean basin as a result of habitat features.