Time-dependent cGMP-activated conductance of detached patches of ROS plasma membrane

cGMP markedly increases the cationic conductance of the 'inside-out' patches of rod outer segment plasma membrane when applied to the inner side. The cGMP-activated conductance of some patches was shown to be time-dependent. The data obtained suggest that the change of cGMP concentration in the near membrane layer underlies this phenomenon rather than the change in the channel's activity. The hydrolysis and, probably, the desorption of the nucleotide are responsible for this.     

Structural organization of kinetoplast DNA and its compactization in a model system in vitro

Studies on compactization and decompactization of the genome are of great importance for elucidation of structural mechanisms taking part in the regulation of gene activity. Kinetoplast DNA (kpDNA) is a convenient model for studies of compactization processes. KpDNA represents unique structure ("network"), consisting of catenated circular molecules of two types: minicircles (900 b.p.) and maxicircles (40 000 b.p.). The compactization process of kpDNA in vitro caused by interaction with synthetic peptide-dansylhydraside trivaline was studied. It was shown that at the initial stages the hairpins are observed on minicircles as if triple rings are being organized. The formation of hairpin is probably favoured by the presence in the minicircles of bent DNA, a specific nucleotide sequence causing rigid bending of the DNA helix. The hairpin does not make contact with the neighbouring DNA segment to form a triple ring, because the sizes of minicircles are too small. The minicircles compactization is finished with a complete collapse of the minicircles with the formation of rod-like structures. The catenation causes branching of rod-like structures. As a result of their intermolecular interaction, the branched rod-like structures become thicker. The process is completed with formation of the compact network, its diameter being 3-6 times smaller compared to the initial one.     

The effect of separate and consecutive administration of cytochrome P-450 inducers to rats on the localization of various isoforms of the enzyme in liver lobe cells

By means of immunohistochemical methods a study of the liver intralobular localization of cytochromes P-450b(+e) and P-450c(+d) has been carried out after separate and consecutive treatment of rats with phenobarbital (PB) and 3-methylcholanthrene (MC). PB-treatment leads to localization of P-450b in the centrilobular region, whereas homogeneous distribution of P-450c in the lobule is observed after MC-treatment. The consecutive treatment with PB and MC is accompanied by the localization of P-450c only in cells of the periportal region of the lobule. PB-treatment of rats after preliminary MC-injection also results in the periportal localization of P-450c, and a small quantity of P-450b is localized in hepatocytes of the centrilobular region. Hence, the consecutive treatment with inducers of different molecular forms of cytochrome P-450 is accompanied by the redistribution of these isoenzymes in parenchymatous cells of the liver lobule. That is confirmed also by biochemical testing and immunochemical analysis of the microsomal fraction of hepatocytes.     

Genetic transformation of mouse cultured cells with the help of high-velocity mechanical DNA injection

NIH 3T3 mouse cells were transfected by the plasmid pSV3neo (G418-resistant) with the help of high-velocity mechanical DNA injection based on the principle of bombarding cells with tungsten particles covered with the DNA. Stable transformants were obtained. Dot-hybridization and Southern analysis revealed the integration into the genome of 5-20 copies per cell of original plasmid DNA. The plasmid DNA was shown to have tandem organization.     

Immunohistochemical localization of cytochrome P-450]

Distribution of different forms of cytochrome P-450 (forms C, D and B) in human placenta by immunohistochemical methods on light microscopy level with colloid gold was studied. Positive reaction with cytoplasm of endothelial cells, called the "epithelioid" plates of chorionic villi was found. Trophoblastic and stromal cells were not stained.     

Role of the commissural channels of the somatosensory system in the conduction of feedback signals during the control of voluntary movements

The time-course of formation of the conditioned defence reflex and electromyograms of the working forelimb were studied on cats with classical and commissural somatosensory pathways transections. It was established that exclusion of the classical somatosensory projections only reduces the rate of the skill formation that is related to the possibility of conducting feedback signals via the remaining commissural pathways. However, the commissural channel in question is not effective enough, since its isolated functioning is accompanied by an increase in the duration of instrumental movement. The combined transection of the classical and commissural somatosensory pathways excludes the possibility of formation of the conditioned reflex on the "deafferented" limb. The lack of direct visual control over the moving forelimb does not essentially affect the behavioral and electromyographic data.     

Big flies, small repeats: the "Thr-Gly" region of the period gene in Diptera

The region of the clock gene period (per) that encodes a repetitive tract of threonine-glycine (Thr-Gly) pairs has been compared between Dipteran species both within and outside the Drosophilidae. All the non- Drosophilidae sequences in this region are short and present a remarkably stable picture compared to the Drosophilidae, in which the region is much larger and extremely variable, both in size and composition. The accelerated evolution in the repetitive region of the Drosophilidae appears to be mainly due to an expansion of two ancestral repeats, one encoding a Thr-Gly dipeptide and the other a pentapeptide rich in serine, glycine, and asparagine or threonine. In some drosophilids the expansion involves a duplication of the pentapeptide sequence, but in Drosophila pseudoobscura both the dipeptide and the pentapeptide repeats are present in larger numbers. In the nondrosophilids, however, the pentapeptide sequence is represented by one copy and the dipeptide by two copies. These observations fulfill some of the predictions of recent theoretical models that have simulated the evolution of repetitive sequences.      

Evolutionary origin of human and primate malarias: evidence from the circumsporozoite protein gene

We have analyzed the conserved regions of the gene coding for the circumsporozoite protein (CSP) in 12 species of Plasmodium, the malaria parasite. The closest evolutionary relative of P. falciparum, the agent of malignant human malaria, is P. reichenowi, a chimpanzee parasite. This is consistent with the hypothesis that P. falciparum is an ancient human parasite, associated with humans since the divergence of the hominids from their closest hominoid relatives. Three other human Plasmodium species are each genetically indistinguishable from species parasitic to nonhuman primates; that is, for the DNA sequences included in our analysis, the differences between species are not greater than the differences between strains of the human species. The human P. malariae is indistinguishable from P. brasilianum, and P. vivax is indistinguishable from P. simium; P. brasilianum and P. simium are parasitic to New World monkeys. The human P. vivax-like is indistinguishable from P. simiovale, a parasite of Old World macaques. We conjecture that P. malariae, P. vivax, and P. vivax-like are evolutionarily recent human parasites, the first two at least acquired only within the last several thousand years, and perhaps within the last few hundred years, after the expansion of human populations in South America following the European colonizations. We estimate the rate of evolution of the conserved regions of the CSP gene as 2.46 x 10(-9) per site per year. The divergence between the P. falciparum and P. reichenowi lineages is accordingly dated 8.9 Myr ago. The divergence between the three lineages leading to the human parasites is very ancient, about 100 Myr old between P. malariae and P. vivax (and P. vivax-like) and about 165 Myr old between P. falciparum and the other two.