The G1 cyclin Cln3p regulates vacuole homeostasis through phosphorylation of a scaffold protein, Bem1p, in Saccharomyces cerevisiae

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dc.contributor.advisor Polymenis , Michael en_US
dc.contributor.committeeMember Chen , Z . Jeffrey en_US
dc.creator Han , Bong Kwan en_US
dc.date.accessioned 2007 -04 -25T20 :08 :09Z
dc.date.accessioned 2014 -02 -19T19 :27 :28Z
dc.date.available 2007 -04 -25T20 :08 :09Z
dc.date.available 2014 -02 -19T19 :27 :28Z
dc.date.created 2005 -12 en_US
dc.date.issued 2007 -04 -25T20 :08 :09Z
dc.identifier.uri http : / /hdl .handle .net /1969 .1 /4795
dc.description.abstract How proliferating cells maintain the copy number and overall size of their organelles is not clear . In the budding yeast Saccharomyces cerevisiae the G1 cyclins Cln1 ,2 ,3p control initiation of cell division by regulating the activity of the cyclin -dependent kinase (Cdk ) Cdc28p . We show that Cln3p controls vacuolar (lysosomal ) biogenesis and segregation . First , loss of Cln3p , but not Cln1p or Cln2p , resulted in vacuolar fragmentation . Although the vacuoles of cln3 ? ? ? ? cells were fragmented , together they occupied a large space , which accounted for a significant fraction of the overall cell size increase in cln3 ? ? ? ? cells . Second , cytosol prepared from cells lacking Cln3p had reduced vacuolar homotypic fusion activity in cell -free assays . Third , vacuolar segregation was perturbed in cln3 ? ? ? ? cells . Our findings reveal a novel role for a eukaryotic G1 cyclin in cytoplasmic organelle biogenesis and segregation . Furthermore we show that the scaffold protein Bem1p , a critical regulator of Cdc42p activity , is a downstream effector of Cln3p /Cdc28p complex . The Cdc42p GTPase is known to be required for vacuole fusion . Our results suggest that Ser72 on Bem1p is phosphorylated by Cdc28p in a Cln3p -dependent manner to promote vacuole fusion . Replacing Ser72 with Asp , to mimic phosphorylation at an optimal Cdkconsensus site located in the first SH3 domain of Bem1p , suppressed vacuolar fragmentation in cells lacking Cln3p . Using in vivo and in vitro assays , we found that Cln3p was unable to promote vacuole fusion in the absence of Bem1p or in the presence of a non -phosphorylatable Bem1p -Ser72Ala mutant . Furthermore , activation of Cdc42p also suppressed vacuolar fragmentation in the absence of Cln3p . Our results provide a mechanism that links cyclin -dependent kinase activity with vacuole fusion through Bem1p and the Cdc42p GTPase cycle . en_US
dc.format.extent 12245318 bytes
dc.format.medium electronic en_US
dc.format.mimetype application /pdf
dc.language.iso en _US en_US
dc.publisher Texas A &M University en_US
dc.subject vacuole en_US
dc.title The G1 cyclin Cln3p regulates vacuole homeostasis through phosphorylation of a scaffold protein , Bem1p , in Saccharomyces cerevisiae en_US
dc.type Book en
dc.type.genre Electronic Dissertation en_US
dc.type.material text en_US
dc.format.digitalOrigin born digital en_US

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The G1 cyclin Cln3p regulates vacuole homeostasis through phosphorylation of a scaffold protein, Bem1p, in Saccharomyces cerevisiae. Available electronically from http : / /hdl .handle .net /1969 .1 /4795 .

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