To achieve accurate gene regulation, some homeodomain proteins bind cooperatively to DNA to increase those site specificities. We report a ternary complex structure containing two homeodomain proteins, aristaless (Al) and clawless (Cll), bound to DNA. Our results show that the extended conserved sequences of the Cll homeodomain are indispensable to cooperative DNA binding. In the AlCll-DNA complex structure, the residues in the extended regions are used not only for the intermolecular contacts between the two homeodomain proteins but also for the sequence-recognition mechanism of DNA by direct interactions. The residues in the extended N-terminal arm lie within the minor groove of DNA to form direct interactions with bases, whereas the extended conserved region of the C-terminus of the homeodomain interacts with Al to stabilize and localize the third a helix of the Cll homeodomain. This structure suggests a novel mode for the cooperativity of homeodomain proteins.

The in¯uence of the spacer structure on the photochemical phase transition behaviour was explored for azobenzene polymer liquid crystals (azo-PLCs) possessing siloxane spacers in the polymer side chain, and for analogue without the siloxane spacer. The photochemical phase transition of the azo-PLC with the siloxane spacer was found to proceed less e ectively than that of the azo-PLC without the siloxane spacer. It was also con® rmed that the spacer structure does not a ect the trans± cis photoisomerizatio n behaviour of the azobenzene moieties. These results were interpreted in terms of stabilization of the alignment of the mesogens in the liquid crystalline phase by the siloxane spacer, since the siloxane chain is one of the most¯exible spacers and decouples the motion of the polymer backbone from that of the aligned mesogens. Furthermore, the response of the azo-PLCs in the photochemical phase transition was evaluated by means of a laser pulse. The phase transition occurred iñ 300 ms for both samples.

In order to improve the separation characteristic at pervaporation, the introduction of several kinds of trialkylsilyl groups into poly ( 1-trimethylsilyl-1-propyne) (PTMSP ) was achieved via metalation of PTMSP followed by treating with trialkylchlorosilanes to afford trialkylsilylated PTMSP. Ratio of TMSP monomer unit and trialkylsilylated unit, x / y , was in the range of 95/5 to 80/20. All the chemically modified PTMSP membranes showed ethanol permselectivity at pervaporation of aqueous ethanol solution. Introduction of appropriate length of alkyl groups (methyl, ethyl, propyl, butyl, hexyl, octyl, and decyl groups) into PTMSP effectively enhanced the selectivity. However, excess introduction of octyl and decyl groups or introduction of dodecyl and octadecyl groups caused decrease of selectivity, of which the value was smaller than that of PTMSP membrane. Furthermore, acetone, acetonitrile, dioxane, and isopropanol were efficiently separated from their aqueous solutions at pervaporation through trimethylsilylated PTMSP membrane. I NTRO DU CTlO NIn the past few years, we have been investigating alcohol permselective membrane for the liquid separation by using pervaporation It is more practical to separate alcohol by alcohol permselective membrane, since it is usually a minor component in the alcohol production, for example, fermentation of biomass such as starch, sugar, and cellulose.Poly ( 1-trimethylsilyl-1-propyne) (PTMSP) has been known to show the greatest permeability coefficients of several gases among the polymer memb r a n e~.~~~ This polymer also has a good membrane forming ability according to its extremely high molecular weight, so that a very thin membrane can be prepared. In addition, PTMSP membrane has also been known to show preferential permeation of ethanol at pervaporation of aqueous ethanol solut i~n .~. ' The separation factor is 10 to 12, when the feed concentration of ethanol is about 7 wt %, and

No abstract

Polyimide/polydimethylsiloxane (PI/PDMS) graft copolymer was prepared following the macromonomer method. First, 3-(3,5-diaminobenzyloxy)propyl-terminated polydimethylsiloxane (DAB-PDMS) was prepared by hydrosilylation of ally1 3,5-dinitrobenzyl ether with hydrosilyl-terminated PDMS, followed by catalytic reduction of the two nitro groups. PI/PDMS graft copolymer was synthesized by polycondensation of DAB-PDMS with 4,4'-oxydianiline (ODA) and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). followed by chemical imidation. The average degree of polymerization of the PDMS chain was in the range between 7 and 25. The resulting graft copolymers were soluble in several organic solvents. Membranes were prepared by solvent casting, followed by heating at 220 "C in vacuo, upon which the membranes became hardly soluble in organic solvents. The gas permeability coefficients of the graft copolymer membranes were much greater than those of the polyimide homopolymer and of the same order as that of a PDMS membrane. Furthermore, a selective permeation of organic liquids, e. g., tetrahydrofuran, acetone and acetonitrile, was observed in the pervaporation of aqueous organic liquids through the copolymer membrane. 0 1992, Huthig & Wepf Verlag, Base1 CCC 0025-1 16)