SEMINAR: �Re-engineering the ribosome for efficient selenoprotein synthesis�

Ross completed his undergraduate degree at the University of Western Australia and joined WAIMR in 2008 where he undertook an honours project in the Laboratory of Synthetic Biology and Drug Discovery supervised by Dr Aleksandra Filipovska and Dr Oliver Rackham. In 2009 he began a PhD (also in the Rackham/Filipovska lab) and has investigated the role of rRNA in controlling the efficiency of selenocysteine incorporation.

The ribosome is a 2.5 MDa molecular machine that converts the information encoded in mRNA into protein, following the rules defined by the genetic code. In all organisms protein composition is limited to 20 amino acids, with the rare exceptions of pyrrolysine and selenocysteine. Although rarely used in the proteome, the incorporation of selenocysteine into proteins is essential for life in many organisms, including humans. The mRNA encoding a selenoprotein has a stem loop known as a SECIS following a UGA stop codon that facilitates the ribosome to introduce selenocysteine at the stop codon. This requires a unique set of factors used only for the synthesis and insertion of selenocysteine (SelA, SelB, SelC and SelD).

The human proteome includes 25 selenoproteins that are mostly uncharacterised because of the inability to express them in bacteria. This is due to the divergence of RNA and protein factors as well as the inherently low efficiency of selenocysteine incorporation in bacteria. We have developed a reporter gene that provides a life/death selection for selenocysteine incorporation and identified mutations in the 16S rRNA which affect the efficiency of the process. This was validated using the endogenous E. coli selenoprotein formate dehydrogenase H. This opens the door for high efficiency site-specific incorporation of selenocysteine and the study of recombinant human selenoproteins. Furthermore the identification of sequences that alter ribosome function provides information on the fundamental biology of protein synthesis.