The G1 Cyclin Cln3p Controls Vacuolar Biogenesis in Saccharomyces cerevisiae

How organelle biogenesis and inheritance is linked to cell division is poorly understood. In the budding yeast Saccharomyces cerevisiae the G1 cyclins Cln1,2,3p control initiation of cell division. Here we show that Cln3p controls vacuolar (lysosomal) biogenesis and segregation. First, loss of Cln3p, but not Cln1p or Cln2p, resulted in vacuolar fragmentation. Although the vacuoles of cln3(delta) cells were fragmented, together they occupied a large space, which accounted for a significant fraction of the overall cell size increase in cln3(delta) cells. Second, cytosol prepared from cells lacking Cln3p had reduced vacuolar homotypic fusion activity in cell-free assays. Third, vacuolar segregation was perturbed in cln3(delta) cells. Our findings reveal a novel role for a eukaryotic G1 cyclin in cytoplasmic organelle biogenesis and segregation.