Recruitment of Cdc28 by Whi3 restricts nuclear accumulation of the G1 cyclin–Cdk complex to late G1

Abstract

The G1 cyclin Cln3 is a key activator of cell-cycle entry in budding yeast. Here we show that Whi3, a negative G1 regulator of Cln3, interacts in vivo with the cyclin-dependent kinase Cdc28 and regulates its localization in the cell. Efficient interaction with Cdc28 depends on an N-terminal domain of Whi3 that is also required for cytoplasmic localization of Cdc28, and for proper regulation of G1 length and filamentous growth. On the other hand, nuclear accumulation of Cdc28 requires the nuclear localization signal of Cln3, which is also found in Whi3 complexes. Both Cln3 and Cdc28 are mainly cytoplasmic during early G1, and become nuclear in late G1. However, Whi3-deficient cells show a distinct nuclear accumulation of Cln3 and Cdc28 already in early G1. We propose that Whi3 constitutes a cytoplasmic retention device for Cln3-Cdc28 complexes, thus defining a key G1 event in yeast cells.

The critical size is set at a single-cell level by growth rate to attain homeostasis and adaptation

“…Briefly, the Cdk-cyclin complex formed by Cln3 [16][17][18][19][20] and Cdc28 21 phosphorylates the transcriptional repressor Whi5 22,23 and activates sBF (swi6/swi4) and mBF (swi6/mbp1) transcription factors 14 to induce the G1/s regulon 15 and trigger cell cycle entry. Whi3 and Ydj1 act as negative and positive regulators, respectively, of release of cyclin Cln3 from the ER [31][32][33] to allow its accumulation in the nucleus. Perhaps, indirectly, Ydj1 could also be required for proper sBF and mBF function (dashed arrow).…”

“…First, we analysed the role of two well-characterized inhibitors of Start: Whi3 and Whi5. Whi3 binds the CLN3 mRNA and contributes to retain the Cdc28-Cln3 complex in the cytoplasm in G1 cells 31,32 . On the other hand, A radial density profile (green line) was used to find two consecutive maximum and minimum pixel values across the cell boundary, which was then arbitrarily established at a pixel which has the value of their arithmetic greyscale mean (see methods for details).…”

Ras/cAMP-dependent Protein Kinase (PKA) Regulates Multiple Aspects of Cellular Events by Phosphorylating the Whi3 Cell Cycle Regulator in Budding Yeast

“…Whi3 function is important not only for control of the G 1 /S transition but also for the switch to developmental options such as invasive growth and meiosis (3,4,6,7). None of the above studies addressed the role of the phosphorylation of Whi3 in such cellular functions.…”

Kinetic partitioning during de novo septin filament assembly creates a critical G1 “window of opportunity” for mutant septin function

“…Whi3 sequesters the mRNA encoding Cln3, the rate-limiting cyclin for G1-S progression. 30,31 Deletion of WHI3 releases Cln3 mRNA and promotes G1-S progression, shortening G1. 30 Our model predicts that whi3D should display strong negative genetic interactions with cdc3(G365R).…”