The actin-nucleating ARP2-ARP3 complex controls cell shape in plants in many different cell types. Its activity is controlled by a multimeric complex containing BRK1 (also known as HSPC300), NAP1, SRA1, ABI and SCAR/WAVE. In this study, we focus on the function of the five putative SCAR homologues in Arabidopsis and we provide biochemical evidence that AtSCAR2 can activate the ARP2-ARP3 complex in vitro. Among the single mutants, mutations in only AtSCAR2 result in a subtle or weak phenotype similar to ARP2, ARP3 and other 'distorted' mutants. Double-mutant analysis revealed a redundancy with AtSCAR4. Systematic application of the yeast two-hybrid system and Bimolecular Fluorescence Complementation (BiFC) revealed a complex protein-interaction network between the ARP2-ARP3 complex and its genetically defined regulators. In addition to protein interactions known in other systems, we identified several new interactions, suggesting that SPIKE1 may be an integral component of the SCAR/WAVE complex and that SCAR proteins in plants might act as direct effectors of ROP GTPases.

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InhaltsubersichtEs wird uber die Synthese einer Reihe einfacher und unsymrtietrisch substitxiierter isomerer ,k?-Thioxoketone und ihrer Ni(l1)-Chclate berichtet.Die Elektronenspektren der Liganden im Bereich yon 250 bis 700 mp und ihre II1-Spektren zwischen 400 und 3800 cm-l sowie die optischen Spcktren der Ni(I1)-Chelate werden beschrieben. Bei den isomeren b-Thioxoketonen werden die regelmaBigen Eigenschaftsanderungenwie Farbe und Schmelzpunkte der Liganden mid ihrer Ni(I1)-Chelate, Elektronenund IR-Spektrenin Abhangigkeit von dem in Nachbarschaft zum Carbonylschwefel befindlichen Substituenten diskutiert. 0 S S 0 1) 111. Mitteilung: G . KLOSE, PH. THOMAS u. E. UHLEMANN, Tetrahedron (im Druck).