The plant circadian clock is proposed to be a network of several interconnected feedback loops, and loss of any component leads to changes in oscillator speed. We previously reported that Arabidopsis thaliana EARLY FLOWERING4 (ELF4) is required to sustain this oscillator and that the elf4 mutant is arrhythmic. This phenotype is shared with both elf3 and lux. Here, we show that overexpression of either ELF3 or LUX ARRHYTHMO (LUX) complements the elf4 mutant phenotype. Furthermore, ELF4 causes ELF3 to form foci in the nucleus. We used expression data to direct a mathematical position of ELF3 in the clock network. This revealed direct effects on the morning clock gene PRR9, and we determined association of ELF3 to a conserved region of the PRR9 promoter. A cis-element in this region was suggestive of ELF3 recruitment by the transcription factor LUX, consistent with both ELF3 and LUX acting genetically downstream of ELF4. Taken together, using integrated approaches, we identified ELF4/ELF3 together with LUX to be pivotal for sustenance of plant circadian rhythms.

The crystal structure of Escherchia coli asparaginase II (EC 3.5.1.1), a drug (Elspar) used for the treatment of acute lymphoblastic leukemia, has been determined at 2.3 A resolution by using data from a single heavy atom derivative in combination with molecular replacement. The atomic model was refined to an R factor of 0.143. This enzyme, active as a homotetramer with 222 symmetry, belongs to the class of a/P proteins. Each subunit has two domains with unique topological features. On the basis of present structural evidence consistent with previous biochemical studies, we propose locations for the active sites between the N-and C-terminal domains belonging to different subunits and postulate a catalytic role for Thr-89.

Physical, chemical and biological stress factors, such as microbial infection, upregulate the transcription levels of a number of plant genes, coding for the so‐called pathogenesis‐related (PR) proteins. For PR proteins of class‐10 (PR‐10), the biological function remains unclear, despite two decades of scientific research. PR‐10 proteins have a wide distribution throughout the plant kingdom and the class members share size and secondary structure organization. Throughout the years, we and other groups have determined the structures of a number of PR‐10 proteins, both in the crystalline state by X‐ray diffraction and in solution by NMR spectroscopy. Despite the accumulating structural information, our understanding of PR‐10 function is still limited. PR‐10 proteins are rather small (~ 160 amino acids) with a fold consisting of three α helices and seven antiparallel β strands. These structural elements enclose a large hydrophobic cavity that is most probably the key to their functional relevance. Also, the outer surface of these proteins is of extreme interest, as epitopes from a PR‐10 subclass cause allergic reactions in humans.

Following the failure of a wide range of attempts to solve the crystal structure of M-PMV retroviral protease by molecular replacement, we challenged players of the protein folding game Foldit to produce accurate models of the protein. Remarkably, Foldit players were able to generate models of sufficient quality for successful molecular replacement and subsequent structure determination. The refined structure provides new insights for the design of antiretroviral drugs.