Studying the 50S Ribosomal Subunit Assembly Process for New Antibiotic Target Discovery Armando Palacios1,2, Amal Seffouh1,2, Dushyant Jahagirdar1,2 and Joaquin Ortega1,2 1Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec H3A 0C7, Canada. 2Centre for Structural Biology, McGill University, Montreal, Quebec H3G 0B1, Canada. The rapid emergence of multi- and pan-drug resistant bacteria across the globe is alarming. It’s estimated that by 2050, ten million people will die each year from infections caused by drug-resistant bacteria. Widespread antibiotic resistance and the lack of new antibiotics has caused researchers to look for new targets to combat bacterial infections. Bacterial ribosome biogenesis is a promising target for new antibiotic development. Despite the ribosome being a common target for antibiotics, its assembly pathway has remained relatively unexplored. YphC is an under characterized and widely conserved enzyme that plays multiple roles in the late-stage assembly of the bacterial 50S ribosomal subunit. Previous studies have revealed biochemical and structural information pertaining to the GTPase function of YphC. We are using microscale thermophoresis and cryogenic electron microscopy to study how and when YphC intervenes in this assembly process. We have found out that it plays a major role in the formation of several important ribosomal landmarks, the central protuberance and the E, P and A sites.