F-Box Protein RcyA Controls Turnover of the Kinesin-7 Motor KipA in Aspergillus nidulans

Abstract

bFungal filamentous growth depends on continuous membrane insertion at the tip, the delivery of membrane-bound positional markers, and the secretion of enzymes for cell wall biosynthesis. This is achieved through exocytosis. At the same time, polarized growth requires membrane and protein recycling through endocytosis. Endocytic vesicles are thought to enter the protein degradation pathway or recycle their content to the cell surface. In Saccharomyces cerevisiae, the Rcy1 F-box protein is involved in the recycling process of a v-SNARE protein. We identified a Rcy1 orthologue, RcyA, in the filamentous fungus Aspergillus nidulans as a protein interacting with the KipA kinesin-7 motor protein in a yeast two-hybrid screen. The interaction was confirmed through bimolecular fluorescence complementation. RcyA possesses an F-box domain at the N terminus and a prenylation (CaaX) motif at the C terminus. RcyA shows also similarity to Sec10, a component of the exocyst complex. The RcyA protein localized to the hyphal tip and forming septa, likely through transportation on secretory vesicles and partially on early endosomes, but independently of KipA. Deletion of rcyA did not cause severe morphological changes but caused partial defects in the recycling of the SynA v-SNARE protein and the positioning of the cell end markers TeaA and TeaR. In addition, deletion of rcyA led to increased concentrations of the KipA protein, whereas the transcript concentration was unaffected. These results suggest that RcyA probably labels KipA for degradation and thereby controls the protein amount of KipA.

The F-box Protein Rcy1 Is Involved in the Degradation of Histone H3 Variant Cse4 and Genome Maintenance

“…RCY1 was originally identified in a screen for genes involved in a endocytic process and was shown to regulate protein trafficking from endosomes to the Golgi network (20,21,29,30). Although yeast Rcy1 was shown to regulate Snc1 ubiquitylation (21) and the Aspergilus nidulans Rcy1 homologue promotes kinesin KipA degradation (31), the physiologic function of Rcy1 in the ubiquitin-proteasome pathway remains elusive. It is possible that the Rcy1-mediated protein trafficking may indirectly affect Cse4 turnover.…”

The Aspergillus nidulans syntaxin PepAPep12 is regulated by two Sec1/Munc‐18 proteins to mediate fusion events at early endosomes, late endosomes and vacuoles

“…8B). In addition, the PGE might recycle membranes containing SynA directly to the plasma membrane, through a pathway involving RcyA (Herrero et al, 2014), whose S. cerevisiae Rcy1p homologue is an effector of the Ypt31p/Ypt32p RAB GTPases (Chen et al, 2005), the orthologues of the A. nidulans exocytic RabE RAB11 (Pantazopoulou et al, 2014).…”

The flippase DnfB is cargo of fimbrin-associated endocytosis inAspergillus nidulans, and likely recycles through the late Golgi

“…Whether DnfB can be polarized through a secondary recycling pathway is unknown. The homolog in yeast, Drs2p, has been shown to act in concert with Rcy1p to support endocytic recycling 22 , but the importance of the A. nidulans Rcy1p homolog, RcyA, in recycling is unclear, 23 and could be resolved in the future. What is clear is that one effect of abolished endocytosis is the likely loss of plasma membrane lipid asymmetry, the consequences of which is a currently unexplored topic in fungal cell biology.…”