Ribosome biogenesis and cell cycle are coordinated processes. Mutations in specific factors that are involved in ribosome biogenesis cause defects in ribosomal RNA processing as well as cell cycle arrest. Recent studies in mammalian cell lines have shown that ribosome biogenesis is linked to tumorgenesis, where mutation or depletion of ribosomal factors, leads to cancer cell proliferation. The yeast Saccharomyces cerevisiae is a useful model organism for understanding the connections between ribosome biogenesis and cell cycle control. Only a handful of studies have been done and these have mainly focused on different transacting factors involved in ribosome biogenesis.

The eukaryote large ribosome subunit, 60S, is comprised of approximately forty eight ribosomal proteins and three ribosomal RNAs. Not a lot of work has been done to elucidate the role of ribosomal proteins, mainly the large subunit ribosomal proteins in cell cycle progression and rRNA processing. I would like to investigate what roles do these r-proteins as well as factors associated with the r-proteins and rRNAs have on these two cellular pathways in Saccharomyces cerevisae. Our lab has found that depleting the ribosomal protein RPL4 of S. cerevisae results in defects in both rRNA processing and cell cycle. This discovery has led us to investigate other ribosomal proteins also have implications in these two cellular pathways.

To analyze effects on the cell cycle, flow cytometric analysis was performed with cells in which synthesis of a specific small or large subunit r-protein had been inhibited. These cells were also analyzed microscopically to look for abnormal cell morphology. We observed that depletion of r-proteins yields a variety of defects in DNA content and cell morphology, depending on the protein analyzed. We are currently characterizing these defects in more detail, analyzing, for example, spindle formation, chromosome segregation, and other cytological markers of the cell cycle.