A comparative study of the degradation of yeast cyclins Cln1 and Cln2

Abstract

The yeast cyclins Cln1 and Cln2 are very similar in both sequence and function, but some differences in their functionality and localization have been recently described. The control of Cln1 and Cln2 cellular levels is crucial for proper cell cycle initiation. In this work, we analyzed the degradation patterns of Cln1 and Cln2 in order to further investigate the possible differences between them. Both cyclins show the same half‐life but, while Cln2 degradation depends on ubiquitin ligases SCFGrr1 and SCFCdc4, Cln1 is affected only by SCFGrr1. Degradation analysis of chimeric cyclins, constructed by combining fragments from Cln1 and Cln2, identifies the N‐terminal sequence of the proteins as responsible of the cyclin degradation pattern. In particular, the N‐terminal region of Cln2 is required to mediate degradation by SCFCdc4. This region is involved in nuclear import of Cln1 and Cln2, which suggests that differences in degradation may be due to differences in localization. Moreover, a comparison of the cyclins that differ only in the presence of the Cln2 nuclear export signal indicates a greater instability of exported cyclins, thus reinforcing the idea that cyclin stability is influenced by their localization.

Comprehensive and quantitative analysis of G1 cyclins. A tool for studying the cell cycle

“…Looking at the cyclin pattern resulting from α-factor synchronization, we can first confirm very low-level and slightly cyclic Cln3 behaviour [33]. Second, Cln1 and Cln2, which are typically plotted as a single curve (for simplification sake), are present in different amounts, as already reported for expression from plasmids [46] and for interference with 3’UTR sequences [47]. Third, our temporal map of Cln expression in relation to START is noticeably different to the current widely used model, with the maximum level reached in the S-phase (Fig 3A).…”

“…This is not entirely surprising, given their morphogenetic role in the polarized growth taking place over a significant period of time within the S-phase [74–76]. Second, we detected substantially differing expression for Cln1 and Cln2 than proposed elsewhere for systems where the 3’UTR was respected [33] or not [46, 47]. Bearing in mind the similarity of the SBF boxes in the promoters of both genes and, consequently, their fairly similar levels of mRNA, it is tempting to speculate that the molecular nature of their differential regulation may depend on the protein sequences, as already suggested elsewhere [14].…”

A transcriptome-wide analysis deciphers distinct roles of G1 cyclins in temporal organization of the yeast cell cycle

“…55–58 . Experimentally, Cln1 and Cln2 show slight differences in expression timing 40 , degradation pattern 59 and nuclear accumulation 13,60 , questioning a full redundancy of the two cyclins.…”

Enhancement of LacI binding in vivo

“…Yeast strains used in the study were derived from W303. The unstable GFP-LacI was generated by fusing with a CLN2 PEST degron, which leads to rapid degradation through the SCF Grr1 –mediated ubiquitination (12). See Supplementary Table SI and II for detailed information of strains and plasmids.…”