The role of Bud23 in the biogenesis of the small ribosomal subunit in Saccharomyces cerevisiae

Ribosomes are the cellular structures responsible for the synthesis of protein in all branches of life. All ribosomes are made from a large and small subunit that in turn are composed of protein and RNA. The synthesis of eukaryotic ribosomes is a complex process involving more than 200 factors and spans three cellular compartments: the nucleolus, the nucloplasm, and the cytoplasm. The precise function of most of these ribosome biogenesis factors remains unknown. The RNA component of ribosomes is in part processed from a large RNA transcript that yields most of the RNA present in mature ribosomes. Part of the maturation process involves modification of this ribosomal RNA as processing is carried out.
Recent work constructing protein interaction networks in Saccharomyces cerevisiae suggested the methyltransferase Bud23 was involved in ribosome biogenesis (1). This thesis describes my work to characterize Bud23 and place it within the ribosome biogenesis pathway. Bud23 is a SAM methyltransferase important for the proper biogenesis of the small ribosomal subunit. Here I will demonstrate that Bud23 methylates G1575 of the small subunit ribosomal RNA (SSU rRNA), and its absence delays export of the SSU rRNA from the nucleolas, and the nucleus, and results in the delayed maturation of the SSU rRNA. Finally, I will show that Bud23 function is connected to small subunit processome factor Utp14 through identification of a Utp14 mutant that suppresses the bud23[Delta] deletion phenotype.