Correlation was positive between the G+C content at the codon third position in vertebrates genes and the G+C content of the genome portion flanking each gene. Analysis of G+C content distribution along DNA sequences using a DNA Date Bank shows that the vertebrate genome is a mosaic of regions with clear differences in their G+C content. The variation in G+C content throughout the genome is discussed in connection with chromosomal banding (G and R bands).
Generation mechanisms of the rhythmic firing patter in the feeding motoneurons innervating the buccal muscles have been studied in several gastropods. The motoneurons are classified into three types depending on their firing phase (P, R1 or R2 phase) during a feeding cycle. It has become apparent that these firing patterns are generated by more than three types of interneurons showing their spike activity during one of the three phases and mediating their excitatory or inhibitory outputs to the motoneurons. Moreover, these interneurons show mutual interactions, suggesting that the basic firing patterns are produced by the interneuronal network. On the other hand, some electrically coupled bursting neurons have been reported in the interneuronal network, suggesting that the basic feeding rhythm is generated by these bursting neurons. Therefore, the neural network of the central pattern generator for gastropod feeding is probably composed of these interneurons and burstiag neurons.
The sea urchin sperm flagella normally beat in a plane. The flagellar beat plane, however, rotates rapidly and reversibly when an appropriate external force is applied by imposing sinusoidal vibration of varying directions on the sperm head. The rotation may involve rotation of the central tubule complex within the flagellum.
Circadian clock is a basic cellular regulatory mechanism for eukaryotic organism and would have a common cellular mechanism. Recent progress in physiological, biochemical and genetical approaches for a mechanism of the clock are briefly reviewed. A regulation of the circadian clock by the light was also reviewed.
In recent years various ionic channels have been reconstituted in planar lipid bilayers by which rigorous analysis of the electrical behavior of single ionic channels can be made. I have reviewed, in the first half of this article, practical techniques for forming planar bilayers and for incorporating channels into them. The second half deals with a structural analysis of the ion conducting pathway of the reconstituted K+ channel from sarcoplasmic reticulum solely by measuring its electrical properties. The electrical analysis of channel structure should be a promissing approach to bridge the gap between the electrical property and the molecular structure of channel proteins in lipid bilayers.
Biological system is consisted of various kinds and states of flow processes of energy, i.e. powers. If a system is able to be subdivided into representable power processes of free energy changes, dissipations and transductions, it is reconstructed as a circuit model by network thermodynamics. Membrane transport system is a typical example which can be synthesized as a model with the modules represented by generalized capacitors, resistors and transformer type transducers. The coupling mechanism in the membrane transport system is well interpreted with the circuit model.
Recently, evidence has been accumulating that the actual molecular mechanism of muscle contraction may be completely different from the widely accepted contraction models by A.F. Huxley (1957) and Huxley and Simmons (1971). Recent experimental results are presented and discussed on the following six topics, i.e., (1) time-resolved X-ray diffraction studies on contracting muscle by use of synchrotron radiation, (2) electron microscopic observation of structural changes of the cross-bridges, (3) weak and strong binding states between the cross-bridges and the thin filaments, (4) distance of a power stroke of the cross-bridges, (5) cooperative interaction of myosin two heads in muscle contraction, and (6) model experiments on muscle contraction by use of the actin cable in plant cells. It is concluded that (1) active structural changes take place in actin molecules in the thin filaments during activation of contraction, (2) the cross-bridges may well keep their 143A periodicity during contraction, (3) the distance over which a cross-bridge can slide the thin filament by the splitting of one ATP molecule may be much larger than that expected from a simple cross-bridge power stroke, and (4) cooperative interactions between the two heads of myosin is necessary for producing force and motion in muscle fibers, though in more simplified systems single-headed myosin can also produce force and motion.