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The three-dimensional structure of the rhodanese homology domain At4g01050(175-195) from Arabidopsis thaliana has been determined by solution nuclear magnetic resonance methods based on 3043 upper distance limits derived from NOE intensities measured in three-dimensional NOESY spectra. The structure shows a backbone root mean square deviation to the mean coordinates of 0.43 A for the structured residues 7-125. The fold consists of a central parallel beta-sheet with five strands in the order 1-5-4-2-3 and arranged in the conventional counterclockwise twist, and helices packing against each side of the beta-sheet. Comparison with the sequences of other proteins with a rhodanese homology domain in Arabidopsis thaliana indicated residues that could play an important role in the scaffold of the rhodanese homology domain. Finally, a three-dimensional structure comparison of the present noncatalytic rhodanese homology domain with the noncatalytic rhodanese domains of sulfurtransferases from other organisms discloses differences in the length and conformation of loops that could throw light on the role of the noncatalytic rhodanese domain in sulfurtransferases.

Ribosomal protein L27 is located near the peptidyltransferase center at the interface of ribosomal subunits, and is important for ribosomal assembly and function. We report the crystal structure of ribosomal protein L27 from Thermus thermophilus HB8, which was determined by the multiwavelength anomalous dispersion method and refined to an R-factor of 19.7% (R(free) = 23.6%) at 2.8 A resolution. The overall fold is an all beta-sheet hybrid. It consists of two sets of four-stranded beta-sheets formed around a well-defined hydrophobic core, with a highly positive charge on the protein surface. The structure of ribosomal protein L27 from T. thermophilus HB8 in the RNA-free form is investigated, and its functional roles in the ribosomal subunit are discussed.

The BolA-like proteins are widely conserved from prokaryotes to eukaryotes. The BolA-like proteins seem to be involved in cell proliferation or cell-cycle regulation, but the molecular function is still unknown. Here we determined the structure of a mouse BolA-like protein. The overall topology is alphabetabetaalphaalphabetaalpha, in which beta(1) and beta(2) are antiparallel, and beta(3) is parallel to beta(2). This fold is similar to the class II KH fold, except for the absence of the GXXG loop, which is well conserved in the KH fold. The conserved residues in the BolA-like proteins are assembled on the one side of the protein.

Escherichia coli DnaA binds to 9 bp sequences (DnaA boxes) in the replication origin, oriC, to form a complex initiating chromosomal DNA replication. In the present study, we determined the crystal structure of its DNA-binding domain (domain IV) complexed with a DnaA box at 2.1 A resolution. DnaA domain IV contains a helix-turn-helix motif for DNA binding. One helix and a loop of the helix- turn-helix motif are inserted into the major groove and 5 bp (3' two-thirds of the DnaA box sequence) are recognized through base-specific hydrogen bonds and van der Waals contacts with the C5-methyl groups of thymines. In the minor groove, Arg399, located in the loop adjacent to the motif, recognizes three more base pairs (5' one-third of the DnaA box sequence) by base-specific hydrogen bonds. DNA bending by approximately 28 degrees was also observed in the complex. These base-specific interactions explain how DnaA exhibits higher affinity for the strong DnaA boxes (R1, R2 and R4) than the weak DnaA boxes (R3 and M) in the replication origin.