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Eukaryotic Cell, February 2007, p. 328-336, Vol. 6, No. 2
1535-9778/07/$08.00+0 doi:10.1128/EC.00203-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
ska,*
Paula Magnelli, and
Phillips W. Robbins
Department of Molecular and Cell Biology, School of Dental Medicine, Boston University, 715 Albany Street, Evans 408, Boston, Massachusetts 02118
Received 27 June 2006/ Accepted 2 November 2006
Chs4p (Cal2/Csd4/Skt5) was identified as a protein factor physically interacting with Chs3p, the catalytic subunit of chitin synthase III (CSIII), and is indispensable for its enzymatic activity in vivo. Chs4p contains a putative farnesyl attachment site at the C-terminal end (CVIM motif) conserved in Chs4p of Saccharomyces cerevisiae and other fungi. Several previous reports questioned the role of Chs4p prenylation in chitin biosynthesis. In this study we reinvestigated the function of Chs4p prenylation. We provide evidence that Chs4p is farnesylated by showing that purified Chs4p is recognized by anti-farnesyl antibody and is a substrate for farnesyl transferase (FTase) in vitro and that inactivation of FTase increases the amount of unmodified Chs4p in yeast cells. We demonstrate that abolition of Chs4p prenylation causes a
60% decrease in CSIII activity, which is correlated with a
30% decrease in chitin content and with increased resistance to the chitin binding compound calcofluor white. Furthermore, we show that lack of Chs4p prenylation decreases the average chain length of the chitin polymer. Prenylation of Chs4p, however, is not a factor that mediates plasma membrane association of the protein. Our results provide evidence that the prenyl moiety attached to Chs4p is a factor modulating the activity of CSIII both in vivo and in vitro.
Published ahead of print on 1 December 2006.
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