A mathematical model for cell sorting and migration in the slug stage of cellular slime molds Dictyostelium discoideum is proposed. Assuming that a slug is a "mixed fluid" of prespore and prestalk cells, a set of equations which describe the dynamics of cell distribution, internal pressure and velocity of the slug are derived from the balance formula of individual cell movement. These equations are analyzed to obtain the stationary distribution pattern of cells, migration velocity and body shape. The existence of critical size of a slug is predicted.
The X-ray structure analysis of HU protein at 2.1Å resolution limit reveals that this protein has an extremely compact body as demonstrated by the % loss of the solvent accessibility area and has a pair of flexible arms. The molecular architecture of the protein suggests the molecular mechanism of DNA binding and folding.
The log P value used for the hydrophobicity parameter, where P is the partition coefficient in a 1-octanol/pH7.0 buffer system, of a number of di-pentapeptides was analyzed with physicochemical parameters for the side chain substituent of component amino acids. The log P value was shown to be governed not only by the "intrinsic" hydrophobicity but also by the steric effect of side chain substituents as well as intramolecular-type solvation and "polar proximity" effects for polar side chains. The β-turn conformational parameters of component amino acids devised from the Chou-Fasman propensity index was nicely applied for the analysis of log P value of tetra-and pentapeptides.
Circular DNA excised mostly by gene rearrangements was isolated from adult thymocytes and splenocytes and cloned into a bacteriophage vector. Analysis of DNA clones showed the lower frequency of T cell receptor (TCR) δ locus compared with the flanking α locus. This suggests that TCR δ locus is successively rearranged from the inside and the excision products are progressively diluted out by the following cell multiplication entailing α gene rearrangements. New V δ subfamilies, special usage of J δ 2, reciprocal joining of two D δ elements and novel sequences homologous to the human δ-gene deleting elements were also found.
Regulation of turor pressure is indispensable to plant cells. In algal cells, turgor pressure is regulated by changing intracellular osmotic pressure via transport of inorganic ions between vacuole and external medium. The brackish water alga, Lamprothamnium succinctum regulate turgor pressure upon hypotonic treatment by releasing K+ and Cl-. We have found that an increase in cytoplasmic free Ca2+ concentration ([Ca2+]c) occurs upon hypotonic treatment. The signal of an increase in turgor pressure may be transduced into this signal, an increase in [Ca2+]c', which would control channel-mediated ion transport from vacuole to extenal medium.
Archaerhodopsin is a light-driven H+ pump of Halobacterium sp. aus-1. Amino acid sequence of archaerhodopsin deduced from the DNA sequence of the archaerhodpsin gene was 59% and 32% homologous to those of bacteriorhodopsin and halorhodopsin in Halobacterium halobium, respectively. The putative trans membrane structures of three retinal proteins were compared and the key residues for ion pumps which are conserved and face to the hydrophilic interior of proteins were suggested.
Molecular mechanism of light-driven proton pump by bacteriorhodopsin was studied by combinations of the site-directed mutagenesis and a varaiety of biochemical and biophysical methods. Using a synthetic bacterio-opsin gene in which 30 unique restriction sites are evenly spaced, we have carried out the extensive amino acid substitutions throughout the entire protein via the cassete mutagenesis. We concluded that Asp-85 and Asp-96 are involved in proton release and uptake step, respectively, and that charged residues including Asp-85, -212, Arg-82 around the protonated Schiff base are essential for determination of the purple color. And we postulated a tertiary structure model of bacteriorhodopsin.