EC Accepts, published online ahead of print on 15 May 2009

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Eukaryotic Cell doi:10.1128/EC.00356-08
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The Saccharomyces cerevisiae Rbg1p protein and its binding partner Gir2, interact on polyribosomes with Gcn1

P. K. Wout, E. Sattlegger, S. M. Sullivan, and J. R. Maddock^*

Department of Molecular, Cellular and Developmental Biology. University of Michigan. Ann Arbor, MI 48109-1048; Institute of Molecular BioSciences, Massey University, Private Bag 102 904 NSMC, Auckland 0632, New Zealand

^* To whom correspondence should be addressed. Email: maddock{at}umich.edu.

Rbg1 is a previously uncharacterized protein of Saccharomyces cerevisiae belonging to the Obg/CgtA subfamily of GTP-binding proteins whose members are involved in ribosome function in both prokaryotes and eukaryotes. Here we show that Rbg1specifically associates with translating ribosomes. In addition, in this study proteins were identified that interact with Rbg1 by yeast two-hybrid screening and include Tma46, Ygr250c, Yap1 and Gir2. Gir2 contains a GI domain similar to that of Gcn2, an essential factor of the general amino acid control pathway required for overcoming amino acid shortage. Interestingly, we found that Gir2, like Gcn2, interacts with Gcn1 through its GI domain, and overexpression of Gir2, under conditions mimicking amino acid starvation, resulted in inhibition of growth that could be reversed by Gcn2 co-overexpression. Moreover, we found that Gir2 also co-fractionated with polyribosomes and this fractionation pattern was partially dependent on the presence of Gcn1. Based on these findings, we conclude that Rbg1 and its interacting partner Gir2 associate with ribosomes, and their possible biological roles are discussed in this work.