The melibiose transport system in Escherichia coli shows versatility in cation coupling. Na⁺, H⁺ or Li⁺ couples to transport depending on substrate in this carrier. To elucidate the relationship between structure and function of the carrier we first determined the primary structure. The carrier consists of 469 amino acid residues with molecular weight of 52, 029. Hydropathy profile of the carrier suggests the presence of about 10 highly hydrophobic regions which probably traverse membrane. There are several hydrophilic regions which may be involved in transport of cations and substrates. We isolated mutants which showed altered cation specificity. We also determined the sequence of mutant carrier, and found replacement of one amino acid residue. This type of approach seems to be useful for understanding of the mechanism of cation coupling.

抄録全体を表示

Organismic behavior can be regarded as adaptive strategies that maximize reproductive success. Recently behavioral ecology has been developing rapidly due to extensive application of mathematical models based on optimal control and game theory.
To illustrate key concepts and techniques, several examples are reviewed:
(1) Emergence pattern of butterflies is analyzed, assuming that each male chooses the optimal emergence date maximizing the number of virgin females he will capture.
(2) Sex ratio pattern in frogs is analyzed, assuming each male frog chooses its schedule of sexual activity through the season.
(3) Plants' growth behavior is modelled as the optimal schedule of material allocation between shoot, root and reproduction.
(4) Tree trunks are explained as a result of a competitive game among trees.
Other examples are briefly summarized. These adaptive strategy models are complementary to mechanistic studies of biological systems.

抄録全体を表示

Specific base sequences have been found in common in genes and regarded as regulatory signals on the level of the primary structure. However DNA constructs higher-order forms in cells and superhelix is an essential structure of DNA in construction of chromatin and in packaging DNA. If DNA is viewed on the basis of superhelix, common features or specific higher-order structures appear among sequences nonhomologous to each other, or far-off sequences are situated side by side. The structural perturbation resulting from negative superhelix induces torsional underwinding which causes local melting, cruciform formation, or conformational shift from B-form to Z-form. Evidence has accumulated which suggests that these comformations of DNA play important roles as recognition and target sites of proteins involved in transcription, replication, and recombination. In addition to the primary structure, superhelix of DNA seems to be a key part of regulatory mechanism of gene expression.
In this article, I will summarize common features of DNA in transcription, and the data on the conformational alteration of double stranded DNA related to regulation of gene expression. I will discuss regulation of gene expression from a view-point of structural perturbation of double helix.

抄録全体を表示

Recent progress in the primary photochemical reaction of rhodopsin studied by picosecond laser photolysis has been reviewed along with a summary on the Visual transduction mechanism in the vertebrate rod receptor cell on the basis of a cGMP hypothesis.
Since picosecond laser photolysis was first applied to the primary photochemical reaction of rhodopsin at 1972, numerous conflicting results have been published about the process for formation of bathorhodopsin or hypsorhodopsin. The disagreement of the results was now explained by considering the energy density of the laser pulse used in these experiments.
Excitation of rhodopsin with a very weak laser pulse, with which the amount of the intermediate produced was proportional to the laser intensity, yielded a new intermediate, photorhodopsin, an immediate precursor of bathorhodopsin. Hypsorhodopsin was not produced under these conditions. It was produced by excitation of rhodopsin with a highly intense laser pulse with which a multiphoton reaction was occurred.
Thus the primary photochemical reaction of rhodopsin at physiological temperature is summarized as follows: On absorption of a photon in the visible region, rhodopsin converts to photorhodopsin through the excited state of rhodopsin. Photorhodopsin decays to bathorhodopsin and then to lumirhodopsin. Hypsorhodopsin may not be an intermediate of rhodopsin under a light-intensity of physiological environment but be produced by photoreaction of photorhodopsin.

抄録全体を表示