Cell cycle arrest caused by CLN gene deficiency in Saccharomyces cerevisiae resembles START-I arrest and is independent of the mating-pheromone signalling pathway.

Abstract

Null mutations in three genes encoding cyclin-like proteins (CLNI, CLN2, and CLN3) in Saccharomyces cerevisiae cause cell cycle arrest in Gl (cln arrest). In clnl cln2 cln3 strains bearing plasmids containing the CLN3 (also called WHII or DAFI) coding sequence under the transcriptional control of a galactose-regulated promoter, shift from galactose to glucose medium (shutting off synthesis of CLN3 mRNA) allowed completion of cell cycles in progress but caused arrest in the ensuing unbudded Gl phase. Cell growth was not inhibited in arrested cells. Cell division occurred in glucose medium even if cells were arrested in S phase during the initial 2 h of glucose treatment, suggesting that CLN function may not be required in the cell cycle after S phase. However, when the coding sequence of the hyperactive C-terminal truncation allele CLN3-2 (formerly DAFI-1) was placed under GAL control, cells went through multiple cycles before arresting after a shift from galactose to glucose. These results suggest that the C terminus of the wild-type protein confers functional instability. cln-arrested cells are mating competent. However, cln arrest is distinct from constitutive activation of the mating-factor signalling pathway because cln-arrested cells were dependent on the addition of pheromone both for mating and for induction of an a-factor-induced transcript, FUSJ, and because MATa/MATa (pheromonenonresponsive) strains were capable of cln arrest in Gl (although a residual capacity for cell division before arrest was observed in MATa/MATa strains). These results are consistent with a specific CLN requirement for START transit.

CDC68, a yeast gene that affects regulation of cell proliferation and transcription, encodes a protein with a highly acidic carboxyl terminus.

“…The rapid decrease in CLN mRNA abundance in cdc68-1 mutant cells may be responsible for the START arrest phenotype exhibited by mutant cells at the restrictive temperature. Indeed, decreased cyclin expression has been previously demonstrated to cause a first-cycle G1 arrest (8,48).…”

“…Recent investigations (8,40,48,66) have revealed the involvement of a family of proteins, termed G1 cyclins, in the activation of the START machinery. Since cells harboring the cdc68-1 mutation are defective in the performance of START (45), we determined whether cdc68-1-mediated arrest involved altered expression of any of the three G1 cyclin genes (8,17,40,48,66). To address this question, transcript levels of the three G1 cyclin genes, CLNJ, CLN2, and CLN3 (previously designated WHI1 [4,40,58] and DAF1 [7]), were examined by Northern analysis ( Fig.…”

Acetyl-CoA induces transcription of the key G1 cyclin CLN3 to promote entry into the cell division cycle in Saccharomyces cerevisiae

“…At the translational level, CLN3 is regulated by TOR (target of rapamycin) and cAMP-protein kinase A (PKA) pathways (25,26) and repressed under various stress conditions (27,28). Cln3p is thought to be a very unstable protein and subjected to ubiquitin-dependent proteolysis (29)(30)(31)(32). Finally, Cln3p protein localization has been reported to be regulated by molecular chaperones Ydj1p and Whi3p (33,34).…”

PP2ACdc55regulates G1cyclin stability

“…8,9 G 1 arrest occurs in the absence of CLN1-3, 10 thus G 1 progression requires the activity of at least one G 1 cyclin. 9,11 All Maintaining accurate progression through the cell cycle requires the proper temporal expression and regulation of cyclins. the mammalian D-type cyclins promote G 1 -S transition.…”