Variability in several ecologic-physiologic traits of different populations of the Asiatic Arctic suslik Citellus parryi]

In several geographic populations of the Arctic ground squirrel C. parryi, studies have been made on changes in oxygen consumption during decrease of the ambient temperature from 25 to 3-4 degrees, thermal preference, hemoglobin content of the blood and composition of the adipose tissue (both brown and white, subcutaneous and visceral). Significant shifts of these indices were found. In animals from various parts of the species area, different sensitivity to cooling was found, as indicated by determinations of oxygen consumption at different temperatures and the prefered temperature: different hemoglobin content of the blood was also found together with differences in the level of two unsaturated fatty acids - the oleic and linoleic ones. Comparison of these data with similar results obtained on various populations of the Siberian ground squirrel C. undulatus revealed obvious differences between these close species with respect to the indices studied.     

Effectiveness of chemical mutagenesis in multiple damage to one or both strands of plasmid DNA

Methods for site-directed multiple modification of DNA have been developed and used for modification of either one or two strands of plasmid DNA. Plasmid DNAs modified in the region of the tet gene were transformed into Escherichia coli cells and Tet colonies were screened. It was shown that multiple lesions in one DNA strand performed using either N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or sodium bisulfite were effectively repaired in the cell by error-free mechanism. In contrast, modification of two DNA strands led to induction of mutations. The efficiency of mutagenesis in the case of modification of a local region of one DNA strand with sodium bisulfite and modification of the other strand with MNNG was 1.1-7.9%. Mutations were analysed by restriction mapping and sequencing. All of them were G----A transitions.     

Cloning of genes for bacterial glycosyltransferases. I. Selection of hybrid plasmids carrying genes for two glucosyltransferases.

A method of identifying plasmids containing genes responsible for synthesis of nucleotide sugar:lipopolysaccharide glycosyltransferases is described. Hybrid ColE1 plasmids containing random fragments of the chromosome of Escherichia coli K12 were introduced into an indicator strain of Salmonella typhimurium which lacks UDP-glucose:lipopolysaccharide glucosyltransferase I due to an rfaG mutation. Plasmids capable of correcting the transferase defect were identified by their ability to convert the bacteriophage sensitivity pattern of the recipient strain from Ffm-sensitive to Ffm-resistant. Analysis of the lipopolysaccharide of the S. typhimurium/ColE1 hybrid strains and assay of cell extracts defined the new enzyme activities. Two plasmids were identified which carried the rfaG+ gene; one of these plasmids also contained genetic information for a second glucosyltransferase, the E. coli glucosyltransferase II, which normally is not present in S. typhimurium.     

Correlation of pause sites in MDV-1 RNA replication with kinetic refolding of the growing chain. A Monte Carlo simulation of the Markov process

We consider a template-instructed MDV-1 RNA replication catalyzed by Q beta replicase. The relaxation of the effective binding of the growing chain to the enzyme is simulated, considering a Markov process where refolding events in the chain are concomitant with chain elongation events. When realistic transition probabilities are considered, it becomes evident that the pause sites in replication are due to relaxation of the binding by folding of the growing chain.     

Metabolic behavior of acetyl glyceryl ether phosphorylcholine on interaction with rabbit platelets

The metabolic fate of 1-O-[³H]alkyl-2-acetyl-sn-glycero-3-phosphorylcholine ([³H]-AGEPC) upon interaction with rabbit platelets was investigated. [³H]AGEPC was converted to a product identified as the long-chain fatty acyl analog. The reaction was unaffected by extracellular calcium. After a lag time of 30 to 60 s the kinetics of the conversion was linear. The rate of the reaction was found to be a function of platelet and AGEPC concentrations. Of the [³H]AGEPC (10^?9m) 85 ± 5% was processed into the-long chain fatty acyl analog within 1 h when incubated at 37 2C with a 1.25 × 10⁹ platelets per milliliter suspension. A maximal number of 1200 to 3600 [³H]AGEPC molecules were converted to the long-chain fatty acyl derivative per minute per platelet in the presence of 2 mm EDTA. Under similar conditions the 1-O-[³H]alkyl-2-(lyso)-sn-glycero-3-phosphorylcholine ([³H]lysoGEPC) also was transformed to a comparable long-chain fatty acyl derivative at a much slower rate and to a lower extent. No significant increase in lysoGEPC was noted in incubation mixtures containing [³H]AGEPC. The possible direct transacylation of AGEPC upon interaction with platelets is discussed as well as the possible involvement of this reaction in directly triggering the platelet response to AGEPC stimuli.     

Effect of primycin on some electric properties of the frog skeletal muscle

The effect of primycin, a guanidine-type antibiotic was studied on the electric properties and 42K+ uptake of the frog sartorius and semitendinosus muscle. Both in normal and choline chloride Ringer solution, primycin evoked a concentration and time dependent depolarization of the surface membrane of the muscle. This depolarization was significantly increased by Na ions. Primycin treatment was shown to evoke a dose-dependent decrease of the depolarization induced by 20 mM K+-Ringer. When the muscles were incubated in a Ringer solution containing choline chloride, during an incubation period of 30 min the uptake of 42K+ was decreased to 12% upon the exposure to 5 x 10(-6) mol primycin as compared to the control value. As the primycin-induced depolarization increased, the shape and amplitude of the action potentials elicited by square-wave electric impulses were altered and decreased, respectively. In sodium isaethionate Ringer 1--2 x 10(-6) M primycin induced a slow depolarization resulting in firing potentials. The results suggest that primycin depolarizes the surface membrane exclusively through the blockade of the resting K+ channels, the other phenomena being the results of this depolarizing effect.