Analysis of r-protein and RNA conformation of 30S subunit intermediates in bacteria.

The ribosome is a large macromolecular complex that must be assembled efficiently and accurately for the viability of all organisms. In bacteria, this process must be robust and tunable to support life in diverse conditions from the ice of arctic glaciers to thermal hot springs. Assembly of the Small ribosomal SUbunit (SSU) of Escherichia coli has been extensively studied and is highly temperature-dependent. However, a lack of data on SSU assembly for other bacteria is problematic given the importance of the ribosome in bacterial physiology. To broaden the understanding of how optimal growth temperature may affect SSU assembly, in vitro SSU assembly of two thermophilic bacteria, Geobacillus kaustophilus and Thermus thermophilus, was compared with that of E. coli. Using these phylogenetically, morphologically, and environmentally diverse bacteria, we show that SSU assembly is highly temperature-dependent and efficient SSU assembly occurs at different temperatures for each organism. Surprisingly, the assembly landscape is characterized by at least two distinct intermediate populations in the organisms tested. This novel, second intermediate, is formed in the presence of the full complement of r-proteins, unlike the previously observed RI* particle formed in the absence of late-binding r-proteins in E. coli. This work reveals multiple distinct intermediate populations are present during SSU assembly in vitro for several bacteria, yielding insights into RNP formation and possible antimicrobial development toward this common SSU target.

Transition metal-substituted Dawson anions as chemo- and regio-selective oxygen transfer catalysts for H2O2 in the epoxidation of allylic alcohols.

Organic-soluble transition metal-substituted Dawson compounds [(n-C(4)H(9))(4)N](9)[P(2)W(17)O(61)M(Br)] (M(n+) = Co(2+), Ni(2+), Cu(2+) and Zn(2+)), [(n-C(4)H(9))(4)N](7)[HP(2)W(17)O(61)M(Br)] (M(n+) = Cr(3+), Mn(3+) and Fe(3+)) and [K/(n-C(4)H(9))(4)N](10-n)[P(2)W(17)O(61)M(H(2)O)] (M(n+) = Ir(4+), Ru(3+) and Pd(2+)) have been investigated as oxygen transfer agents for H(2)O(2) to a series of primary allylic alcohols to generate epoxides under biphasic reaction conditions (1,2-dichloroethane/H(2)O) at 30 or 35 degrees C, such that the effect of variations in the substituted transition metals could be evaluated. The allylic alcohols involved the species R(1)R(2)C=C(R(3))CH(2)-OH (where R(1), R(2) and R(3) = H or Me), as well as cyclic (2-cyclohexen-1-ol), bicyclic [(R-)-(-)-myrtenol and (R-)-(-)-nopol] and species with two unsaturated sites (geraniol and nerol). The reactions are highly chemoselective and regioselective. The order of reactivity for the M(II)-substituted species is Pd(II) > Zn(II) > Co(II) > Ni(II), and for M(III) and M(IV) substitution is Mn(III) approximately Ir(IV) > Fe(III) > Cr(III). The observed orders are consistent with the formation of metal(n+)-alcohol species as part of the reaction mechanism. For the more polarizing Ir(IV), however, Ir(IV)-alcoholate species are likely involved in the mechanism. Formation constants for the Mn(III) and Co(II)-phosphopolyoxotungstate-alcohol species with all of the above alcohols have been evaluated in 1,2-dichloroethane at 25 degrees C and range from 19.0-3.5 M(-1). The most likely transition state involves coordination of the alcohol to the transition metal substituted at the lacunary site, or alkoxide in the case of Ir(IV), along with interaction of the double bond of the alcohol with a peroxo group located at a W(VI) site adjacent to the substituted transition metal.