Function of the atypical RIO kinases in late stages of the maturation of pre-40S particles in yeast and human cells

Two atypical kinases of the Rio family, Rio1p and Rio2p, are specifically required for pre-40S particle maturation in yeast. Rio1p likely intervenes at a very late step in the cytoplasm, just prior to the final maturation of 20S pre-rRNA into 18S rRNA by the Nob1p endonuclease. We are accumulating evidence that pre-40S particles produced in yeast cells lacking Rio1p can initiate translation and we are investigating whether such particles can support translation elongation and/or translate a specific subset of mRNAs. We are also investigating the impact of post-translational modifications of the human counterpart of yeast Rio2p, RIOK2. Our preliminary results indicate that hRIOK2 is phosphorylated by kinases that regulate cell growth and proliferation in humans, hinting that signal transduction pathways may directly regulate pre-40S particle maturation. To investigate this hypothesis, we will use molecular and cellular biological techniques, as well as genetics and proteomics to identify the hRIOK2 phosphorylation site(s), the signaling pathways and kinases involved, and the consequences of these phosphorylation events on ribosome biogenesis.