Peculiarities of the B to A transition of the lambda phage regulatory site OR3 and of its fragment

Conformations of the synthetic deoxyoligonucleotide 17 base pairs long, which is an OR3 operator of lambda phage, and of its 9-b.p. fragment were studied by the circular dichroism method (CD). The regions of stability of the double-stranded state were determined for these duplexes. A comparison of the CD spectra for these oligonucleotides with the CD for a lengthy DNA showed the conformation of these short DNA pieces to belong to the B-family. A cooperative change in the CD spectra is observed in trifluoroethanol (TFE) solutions at a TFE concentration specific for each oligonucleotide, which is supposed to stem from a B to A transition. The length of the fragment was found to affect the ability for the B-A transition. The transition into the A form is hindered by 13% TFE for the short 9-nucleotide in comparison with the 17-nucleotide. We suggest that this is due to the B form stabilization by terminal base pairs (B-phility of the ends).     

Unusual genome organization of the marine invertebrate Rapana thomasiana Grosse (Gastropoda)

The genome organization of the marine snail Rapana thomasiana Grosse (Gastropoda), genome size 2.7 pg, was studied by reassociation kinetics, S₁-nuclease assay, and restriction enzyme analysis. The slow-reassociating (single-copy) fraction represented only 21% of the genome. The average length of 80% of the single-copy sequences was less than 700 bp and the remaining 20% no longer than 1,400 bp. Longer stretches of unique DNA were not observed. The genome contained an unusually high percent-age of inverted repeats: at standard fragment length the zero-time binding fraction amounted to 25% of the genome. Foldback structures ranging from 200 bp to more than 10 kb were observed after S₁-nuclease treatment. They were randomly distributed throughout at least 85% of the genome, and the spacings between them were estimated to be about 1,600 bp on the average. The middle-repetitive DNA (45% of the genome) contained two kinetic components, repeated 430 and 65,000 times per genome, respectively. It was found that the majority of the repetitive sequences are about 300 bp long. Longer repeats (about 2,000 bp) were also observed, comprising a small portion of the genome. The inverted repeats, the middle-repetitive, and the singly-copy sequences were fully interspersed in the genome, thus indicating that R. thomasiana DNA is not organized in either the Xenopus or the Drosophila pattern type. — R. thomasiana is the only mollusc so far in which a satellite DNA has been found. It is organized in tandem repeats of 1,460 bp with a very complex organization but a low degree of divergence.     

Formation of the respiratory enzyme apparatus in plant cells. III. Antigenic spectra of mitochondria in the root tip of corn

By means of one- and two-dimensional (cross) immunoelectrophoresis, immunoelectro-diffusion and radial immunodiffusion, about 20 antigens were detected in mitochondria of meristem, zone of elongation and mature cells, among which some were identified by zymographic methods. The differentiation of root cells is not accompanied by qualitative changes in antigenic spectra of mitochondria and changes in the ratio of antigens (including glutamate and malate dehydrogenases) suggest that mature mitochondria develop from preexisting ones by gradual quantitative changes which are due to different rate of synthesis of constituent proteins.     

The action of membranotropic compounds with various structures on the parameters of the phase transition of dimyristoylphosphatidylcholine

The effect of substances of different nature on the thermodynamic characteristics of dimyristoylphosphatidylcholine (DMPC) phase transition by the differential scanning microcalorimetry has been studied. The substances disposed in hydrophobic part of membrane--alpha-tocopherol, ubiquinone Q10, ionol and vitamin K3 cause the decrease of enthalpy and cooperativity of phase transition. The substances which have the side hydrocarbon chain (tocopherol and ubiquinone Q10) compared with ones without it (ionol and vitamin K3) and reduced quinones (Q10 and vitamin K3) compared with the oxidized ones have stronger influence on the enthalpy and cooperativity of transition. The inclusion of the local anesthetic dicaine disposed mainly in the zone of polar heads of phospholipids into DMPC membranes decreases the temperature of phase transition considerably and practically does not change the cooperativity. A possibility to use the method of differential scanning microcalorimetry to estimate the localization of membrane tropic substances within lipid bilayer is under discussion.     

Endolyn-78, a membrane glycoprotein present in morphologically diverse components of the endosomal and lysosomal compartments: implications for lysosome biogenesis

A monoclonal antibody (2C5) raised against rat liver lysosomal membranes was used to identify a 78-kD glycoprotein that is present in the membranes of both endosomes and lysosomes and, therefore, is designated endolyn-78. In cultures of rat hepatoma (Fu5C8) and kidney cells (NRK), this glycoprotein could not be labeled with [35S]methionine or with [32P]inorganic phosphate but was easily labeled with [35S]cysteine and [3H]mannose. Pulse-chase experiments and determinations of endoglycosidase H (endo H) sensitivity showed that endolyn-78 is derived from a precursor of Mr 58-62 kD that is processed to the mature form with a t1/2 of 15-30 min. The protein has a 22-kD polypeptide backbone that is detected after a brief pulse in tunicamycin-treated cells. During a chase in the presence of the drug, this is converted into an O-glycosylated product of 46 kD that despite the absence of N-linked oligosaccharides is effectively transferred to lysosomes. This demonstrates that the delivery of endolyn-78 to this organelle is not mediated by the mannose-6-phosphate receptor (MPR). Immunocytochemical experiments showed that endolyn-78 is present in the limiting membranes and the interior membranous structures of morphologically identifiable secondary lysosomes that contain the lysosomal hydrolase beta-glucuronidase, lack the MPR, and could not be labeled with alpha-2-macroglobulin at 18.5 degrees C, a temperature which prevents appearance of endocytosed markers in lysosomes. Endolyn-78 was present at low levels in the plasma membrane and in peripheral tubular endosomes, but was prominent in morphologically diverse components of the endosomal compartment (vacuolar endosomes and various types of multivesicular bodies) which acquired alpha-2-macroglobulin at 18.5 degrees C, and frequently contained substantial levels of the MPR and variable levels of beta-glucuronidase. On the other hand, the MPR was very rarely found in endolyn-containing structures that were not labeled with alpha-2-macroglobulin at the low temperature. Thus, the process of lysosomal maturation appears to involve the progressive delivery of lysosomal enzymes to various types of endosomes that may have already received some of the lysosomal membrane proteins. Although endolyn-78 would be one of the proteins added early to endosomes, other lysosomal membrane proteins may be added only to multivesicular endosomes that represent very advanced stages of maturation.     

Estimate of the quantum value variability in excitatory synapses of CA1 area in hippocampal slices and its effects on the quantum value estimate

Excitatory postsynaptic potentials (EPSPs) evoked by near-threshold stimulation of the radial layer were recorded from the CA1 area of guinea pig hippocampal slices. An optimization method based on the deconvolution technique was used to reconstruct a noise-free discrete distribution of the amplitudes with regular (quantal) intervals (v) between the discrete components. The standard deviation of v (Sv) was studied for its effect on the estimate of the v value. Twenty-two amplitude distributions with approximately regular, visually distinguishable peaks were analyzed. It was found that, in some cases, too small (<0.1–0.15 v) or too large (>0.3–0.4 v) Sv led to lower v estimates in comparison with those obtained for Sv in the range of 0.1–0.3 v. Computer experiments have shown that too small or too large Sv values may lead to underestimates of the stimulated v values. The average underestimate for physiological data is probably 10–15%, but, in some cases, it may be higher. Judging from a maximal verisimilitude criterion, optimal v estimates are obtained for Sv between 0 and 0.15 v. Comparison of simulated and physiological data suggests that the variation coefficient of v for hippocampal synapses formed by radial fibers on CA1 neurons is equal to 0.1–0.2 Sv values generally accepted for the deconvolution procedure (0 or 0.05 v) seem to be underestimated for central synapses, while Sv>0.3 v are overestimated. Underestimates of Sv known from literature may be due to a dependence of the deconvolution procedure results on the noise level, as well as due to a probable nonlinear interaction between the signal and noise. Overestimates may be a result of multiple spontaneous quantal release.Translated from Neirofiziologiya, Vol. 25, No. 1, pp. 10–17, January–February, 1993.     

The targeted force steps developed by a human wrist: Cyclic components in the motor program

The targeted flexor isometric force steps developed by a wrist and corresponding EMG activity of the flexor muscles were studied in healthy volunteers. In 82.3–97.5% of trials, the main component of the force trajectory (before the postcorrections of the force level) showed complex dynamics: several (from two to five)dF/dt peaks were observed at this section of the trajectory. The distribution of time intervals from the initiation of the force trajectory todF/dt peaks was polymodal in all cases. The mean interval between successivedF/dt peaks varied from 56.7 msec to 84.4 msec in different individuals (the average group value was 70.5 msec). All tested subjects exhibited amplitude modulation of integrated EMG at the section reflecting the force step development; the averaged interval between the successive first-order EMG peaks calculated for the group of five persons was 78.6 msec. Strict temporal correlation ofdF/dt peaks and EMG peaks was found (coefficient of correlation averaged 0.94). It is concluded that the motor command ensuring performance of isometric force step includes a cyclic component; this feature must be taken into account when mechanisms controlling such motor events are interpreted. The frequency of the component is near the upper limit of a normal tremor frequency band. At the same time, it is impossible to regard the cyclic component in the motor command as a result of simple superposition of tremor on the targeted force development because the cyclic component is clearly synchronized with the force step initiation.Neirofiziologiya/Neurophysiology, Vol. 25, No. 6, pp. 455–462, November–December, 1993.     

Microelectrophoretic and 9-Aminoacridine Fluorescence Study of the Surface Electrical Properties of Suspension Cultured Catharanthus roseus Cells and Isolated Protoplasts: Effects of Abscisic Acid Treatment

The effects of abscisic acid (ABA) treatments on the surfaceelectrical properties of cells and isolated protoplasts fromCatharanthus roseus cell suspension cultures were studied byelectrophoretic mobility and 9-aminoacridine (9AA) fluorescencemeasurements. The surface charge densities of the cells andprotoplasts estimated from electrokinetic data were –0.064Cm^–2and –0.048 C m^–2 respectively. These values wereclose to that estimated by 9AA fluorescence technique i.e.,–0.053 Cm^–2 for the cells and –0.041 Cm^–2for the isolated protoplasts accordingly. The net negative surfacecharge density decreased after application of 10 µM and50 µM ABA in both cells and protoplats, the more pronouncedeffect being observed at 10 µM ABA. When 100 µMABA was supplemented to the cell suspension culture the oppositeeffect was observed. The average charge density increased to–0.074 C m^–2 for the cells, and to –0.055C m^–2 for protoplasts, as revealed from the 9AA measurements.The results are discussed in terms of specific concentrationdependent ABA-induced alterations of the electrostatic propertiesof cell and protoplast membranes. (Received December 12, 1994; Accepted April 3, 1995)