Distinct mechanisms control the stability of the related S-phase cyclins Clb5 and Clb6.

Journal Article (Journal Article)

The yeast S-phase cyclins Clb5 and Clb6 are closely related proteins that are synthesized late in G1. Although often grouped together with respect to function, Clb5 and Clb6 exhibit differences in their ability to promote S-phase progression. DNA replication is significantly slowed in clb5Delta mutants but not in clb6Delta mutants. We have examined the basis for the differential functions of Clb5 and Clb6 and determined that unlike Clb5, which is stable until mitosis, Clb6 is degraded rapidly at the G1/S border. N-terminal deletions of CLB6 were hyperstabilized, suggesting that the sequences responsible for directing the destruction of Clb6 reside in the N terminus. Clb6 lacks the destruction box motif responsible for the anaphase promoting complex-mediated destruction of Clb5 but contains putative Cdc4 degron motifs in the N terminus. Clb6 was hyperstabilized in cdc34-3 and cdc4-3 mutants at restrictive temperatures and when S/T-P phosphorylation sites in the N terminus were mutated to nonphosphorylatable residues. Efficient degradation of Clb6 requires the activities of both Cdc28 and Pho85. Finally, hyperstabilized Clb6 expressed from the CLB6 promoter rescued the slow S-phase defect exhibited by clb5Delta cells. Taken together, these findings suggest that the SCF(Cdc4) ubiquitin ligase complex regulates Clb6 turnover and that the functional differences exhibited by Clb5 and Clb6 arise from the distinct mechanisms controlling their stability.

Full Text

Duke Authors

Cited Authors

  • Jackson, LP; Reed, SI; Haase, SB

Published Date

  • March 2006

Published In

Volume / Issue

  • 26 / 6

Start / End Page

  • 2456 - 2466

PubMed ID

  • 16508019

Pubmed Central ID

  • PMC1430301

Electronic International Standard Serial Number (EISSN)

  • 1098-5549

International Standard Serial Number (ISSN)

  • 0270-7306

Digital Object Identifier (DOI)

  • 10.1128/mcb.26.6.2456-2466.2006


  • eng