High impact information on HOF1

• SCF(Grr1)-mediated degradation of Hof1 may thus represent a novel mechanism to couple exit from mitosis with initiation of cytokinesis [1].
• While Hof1 is required early in mitosis to assemble a functional actomyosin ring, it is specifically degraded late in mitosis and remains unstable during the entire G1 phase of the cell cycle [1].
• During cytokinesis, however, the Cyk2 double ring merges with the actomyosin ring and exhibits a contraction-like size change that is dependent on Myo1p [2].
• Dual function of Cyk2, a cdc15/PSTPIP family protein, in regulating actomyosin ring dynamics and septin distribution [2].
• These observations suggest that the septin-containing ring is dynamically distinct from the actomyosin ring and that Cyk2p transits between the two types of structures [2].

Biological context of HOF1

• Around telophase, Hof1p is phosphorylated and the double rings merge into a single ring that contracts slightly and may colocalize with the actomyosin structure [3].
• Video microscopy of cells expressing green fluorescent protein (GFP)-tagged Cyk2p revealed that Cyk2p forms a double ring that coincides with the septins through most of the cell cycle [2].
• Deletion of either cyk3 or hof1 alone results in a mild cytokinetic phenotype [5-7], but deletion of both genes resulted in lethality and a complete cytokinetic block, suggesting overlapping function [4].
• Our results also show that downregulation of Hof1 at the end of mitosis is necessary to allow efficient contraction of the actomyosin ring and cell separation during cytokinesis [1].
• Furthermore, we found that, in the absence of actin overexpression, a novel, Hof1-dependent actin belt is formed at the bud neck of anaphase cells [5].

Physical interactions of HOF1

• Vrp1p binds an SH3-domain-containing fragment of Hof1p in vitro [6].

Regulatory relationships of HOF1

• Overexpression of Cyk2p also blocks cytokinesis, most likely due to a loss of the septins from the bud neck, indicating that Cyk2p may also play a role in regulating the localization of the septins [2].

Other interactions of HOF1

• Hof1p localization is dependent on septins but not Myo1p [3].
• Synthetic lethality suggests that Bni1p and Myo1p belong to one functional pathway, whereas Hof1p and Bnr1p belong to another [3].
• Vrp1p functions in both actomyosin ring-dependent and Hof1p-dependent pathways of cytokinesis [6].
• These results indicate that Bnr1p directly interacts with Hof1p as well as with profilin to regulate cytoskeletal functions in S. cerevisiae [7].
• Interaction of Bnr1p with a novel Src homology 3 domain-containing Hof1p. Implication in cytokinesis in Saccharomyces cerevisiae [7].

Analytical, diagnostic and therapeutic context of HOF1

• Upon septum formation, Hof1p splits into two rings, disappearing upon cell separation [3].

References