title: Ribosome biogenesis is sensed at the Start cell cycle checkpoint.
abstract: In the yeast Saccharomyces cerevisiae it has long been thought that cells must reach a critical cell size, called the "setpoint," in order to allow the Start cell cycle transition. Recent evidence suggests that this setpoint is lowered when ribosome biogenesis is slowed. Here we present evidence that yeast can sense ribosome biogenesis independently of mature ribosome levels and protein synthetic capacity. Our results suggest that ribosome biogenesis directly promotes passage through Start through Whi5, the yeast functional equivalent to the human tumor suppressor Rb. When ribosome biogenesis is inhibited, a Whi5-dependent mechanism inhibits passage through Start before significant decreases in both the number of ribosomes and in overall translation capacity of the cell become evident. This delay at Start in response to decreases in ribosome biogenesis occurs independently of Cln3, the major known Whi5 antagonist. Thus ribosome biogenesis may be sensed at multiple steps in Start regulation. Ribosome biogenesis may thus both delay Start by increasing the cell size setpoint and independently may promote Start by inactivating Whi5.
authors.affiliation: Department of Genetics, Yale University School of Medicine, New Haven, CT 06520, USA.
authors.forename: Kara A
authors.initials: KA
authors.lastname: Bernstein
authors.forename: Franziska
authors.initials: F
authors.lastname: Bleichert
authors.forename: James M
authors.initials: JM
authors.lastname: Bean
authors.forename: Frederick R
authors.initials: FR
authors.lastname: Cross
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Baserga
mesh_terms: D002467:Cell Nucleus / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D016193:G1 Phase; D049452:Green Fluorescent Proteins / Q000378:metabolism; D014176:Protein Biosynthesis; D012322:RNA Precursors / Q000378:metabolism; D012331:RNA, Fungal / Q000378:metabolism; D012337:RNA, Ribosomal, 18S / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D012269:Ribosomal Proteins; D012270:Ribosomes / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D013997:Time Factors; D014617:Vacuoles / Q000378:metabolism
chemical_list: C079895:CLN3 protein, S cerevisiae; D016213:Cyclins; C100850:PWP2 protein, S cerevisiae; D012322:RNA Precursors; D012331:RNA, Fungal; D012337:RNA, Ribosomal, 18S; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; C508130:Whi5 protein, S cerevisiae; D049452:Green Fluorescent Proteins