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The higher plant Arabidopsis thaliana (Arabidopsis) is an important model for identifying plant genes and determining their function. To assist biological investigations and to define chromosome structure, a coordinated effort to sequence the Arabidopsis genome was initiated in late 1996. Here we report one of the first milestones of this project, the sequence of chromosome 4. Analysis of 17.38 megabases of unique sequence, representing about 17% of the genome, reveals 3,744 protein coding genes, 81 transfer RNAs and numerous repeat elements. Heterochromatic regions surrounding the putative centromere, which has not yet been completely sequenced, are characterized by an increased frequency of a variety of repeats, new repeats, reduced recombination, lowered gene density and lowered gene expression. Roughly 60% of the predicted protein-coding genes have been functionally characterized on the basis of their homology to known genes. Many genes encode predicted proteins that are homologous to human and Caenorhabditis elegans proteins.

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The dependence of the properties of the three-phase bodies in ternary H20-oil-nonionic amphiphile mixtures on the nature of the oil and the amphiphile is of importance for both research and application.We suggest characterizing these properties by the coordinates 71* (temperature) and 7* (amphiphile weight fraction) of the amphiphile-rich phase (the microemulsion) at equal volumes of water and oil, as well as by the interfacial tension crabl between the aqueous and the oil-rich phase at this point of the phase prism. A relation between these properties is suggested that permits evaluating one of them if the other two are known. Furthermore, it is shown that the dependence of T* on the nature of the oil and the amphiphile is apparently correlated with that of the critical temperatures of the two binary mixtures oil-amphiphile and H20-amphiphile. The results are briefly discussed with respect to the currently proposed phenomenological models of microemulsions.

In part 1 of this series (ref 1) we presented a qualitative thermodynamic description of the phase behavior of quaternary mixtures of water, nonpolar solvents, nonionic amphiphiles, and salts. The phase behavior of such mixtures follows general patterns that are essentially determined by the phase diagrams of the corresponding binary and ternary mixtures. In this paper (part 2) the nonionic amphiphiles are replaced by ionic amphiphiles. The general patterns of these mixtures, in particular the phase sequence with rising temperature, are inverse to those with nonionic amphiphiles? It is shown that this inverse behavior originates from the difference between the phase diagrams of binary H20-nonionic amphiphile and those of H20-ionic amphiphile mixtures.