Abstract
Previous studies have revealed many parallels in the cell cycle regulation of the Ace2 and Swi5 transcription factors. Although both proteins begin entry into the nucleus near the start of mitosis, here we show that Ace2 accumulates in the nucleus and binds DNA about 10 min later in the cell cycle than Swi5. We used chimeric fusions to identify the N-terminal region of Ace2 as responsible for the delay, and this same region of Ace2 was required for interaction with Cbk1, a kinase necessary for both transcriptional activation by Ace2 and asymmetric distribution of Ace2. Ace2 and Swi5 also showed differences in prevalence during the cell cycle. Swi5 is apparently degraded soon after nuclear entry, whereas constant Ace2 levels throughout the cell cycle suggest Ace2 is exported from the nucleus. Our work suggests that the precise timing of Ace2 accumulation in the nucleus involves both a nuclear export sequence and a nuclear localization signal, whose activities are regulated by phosphorylation.
Highlights
The mechanisms controlling the cell cycle regulation of Ace2 and Swi5 have been investigated
Regions A/B of Ace2 Are Required for Cbk1-dependent Activation and Cbk1 Interaction—The CBK1 gene encodes a protein kinase that interacts with Ace2, and cbk1 mutations change the localization of Ace2 and reduce expression of genes activated by Ace2 [20, 22, 24]
We examined the Swi5 protein, as Swi5 and Ace2 are related transcription factors with similar patterns of cell cycle regulation, and determined that a cbk1 mutation has little effect on Swi5 protein
Summary
The mechanisms controlling the cell cycle regulation of Ace2 and Swi5 have been investigated. We used protein chimeras between Ace2 and Swi5 to identify regions A/B of Ace2 as important for this cell cycle delay, and these regions were required for daughter-specific localization and for responsiveness to the Cbk1 kinase. We have described chimeric fusions between Ace2 and Swi5 and how specific portions of the non-conserved N-terminal regions contribute to transcriptional activation of specific target genes [15] (Fig. 1A).
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