Construction and analysis of base-paired regions of the 16S rRNA in the 30S ribosomal subunit determined by constraint satisfaction molecular modelling

Biochemical and molecular identification and characterization of lactic acid bacteria and yeasts isolated from Ethiopian naturally fermented buttermilk

Lactic acid bacteria (LAB) and yeasts were enumerated and identified from naturally fermented buttermilk. Isolates were first subjected to chemical tests and then to molecular characterization. Molecular identification involved pure sequencing of 16s rRNA (LAB) and 18s rRNA (yeast) genes. Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (DGGE) was used for detection of microbiota composition. Eighty-five LAB and 26 yeast isolates obtained from 16 small-scale dairy farms were isolated and identified. The microbial composition was dominated by strains of Lactococcus lactis ssp. lactis, Lactobacillus plantarum and Saccharomyces cerevisiae. Molecular techniques enabled not only genetic confirmation but also detection of some uncultivated strains. The presence of diverse strains of LAB and yeasts in NFB indicated a potential for development of different starter cultures to make new dairy products.

Mapping structural differences between 30S ribosomal subunit assembly intermediates

Under appropriate conditions, functional Escherichia coli 30S ribosomal subunits assemble in vitro from purified components. However, at low temperatures, assembly stalls, producing an intermediate (RI) that sediments at 21S and is composed of 16S ribosomal RNA (rRNA) and a subset of ribosomal proteins (r-proteins). Incubation of RI at elevated temperatures produces a particle, RI*, of similar composition but different sedimentation coefficient (26S). Once formed, RI* rapidly associates with the remaining r-proteins to produce mature 30S subunits. To understand the nature of this transition from RI to RI*, changes in the reactivity of 16S rRNA between these two states were monitored by chemical modification and primer extension analysis. Evaluation of this data using structural and biochemical information reveals that many changes are r-protein-dependent and some are clustered in functional regions, suggesting that this transition is an important step in functional 30S subunit formation.

Large-scale motions within ribosomal 50S subunits as demonstrated using photolabile oligonucleotides

Photolabile oligonucleotides (PHONTs) bind to rRNA sequences to which they are complementary and, on photolysis, incorporate into neighboring ribosomal components. Here we report on photocrosslinking results obtained with PHONTs targeting 23S rRNA nucleotides 1882-1892, in the long lateral arm of the 50S subunit (PHONT 1892), and 1085-1093, in the L11 binding domain (PHONT 1093). Photolysis of the PHONT 1892.50S and PHONT 1093.50S complexes leads to formation of 'long-range' crosslinks from C1892 to U1094/A1095 and G1950, and from G1093 to U1712/1716 and U1926, that are clearly incompatible with published crystal structures of 50S subunits. These results provide strong evidence that within the 50S subunit (a) the L11 binding domain can extend in an arm-like fashion, accessing large areas of the ribosome, and (b) the lateral arm can bend about the noncanonical helix at its center. Such motions may have functional relevance in identifying regions that undergo major conformational change as the ribosome moves through its catalytic cycle.