3. Factor mediated regulation of ribosome biogenesis

In bacteria, the 70S ribosome is composed of two subunits, a small 30S subunit and a large 50S subunit. Each subunit is composed of ribosomal RNA and ribosomal proteins. In E. coli for example, the 30S subunit contains a single 1542 nucleotide (nt) 16S rRNA and 21 small subunit r-proteins, whereas the 50S subunit contains two RNAs, a 115 nt 5S rRNA and 2904 nt 23S rRNA, together with 33 large subunit r-proteins. The synthesis of ribosomes is one of the major tasks of the cell, particularly in actively growing bacteria, where ribosomes can constitute up to 30 % of the dry mass of the cell, whereas in eukaryotes they represent no more than 5 %. Therefore the ability to rapidly regulate the synthesis of nascent ribosomal particles provides an important advantage to the cell. Thus, one of the challenges for the E. coli cell is to coordinate both the synthesis of r-proteins and rRNA as well as the binding of the >50 r-proteins to the >4500 nts rRNA in the correct manner and order to ensure formation of active particles. Although bacterial ribosomal subunits can be reconstituted in vitro from purified rRNA and r-protein components, the conditions required to do this, namely high magnesium and long incubations at elevated temperatures, are far from physiological. Instead, in vivo a plethora of protein factors are involved to facilitate the assembly process. In bacteria, a number of protein factors have been identified that are involved in processing, such as RNases and helicases, or modification of the ribosomal components by methylases, acetylases and pseudouridinylases, however accumulating evidence suggests that there are in fact many more protein factors that appear to be directly involved in the assembly process. These include factors that bind to the small 30S subunit, such as RimM, RbfA, Era, as well as to the large 50S ribosomal subunit, including Obg, Der and YlqF. The Wilson group is interested in structurally characterizing the interaction of these factors with the ribosome and understanding how they facilitate assembly of the respective ribosomal particle. Moreover, since many of these factors appear to be highly conserved and in many cases specific for bacteria, they are considered as emerging targets for new antimicrobial drugs.