The yeast protein Mrs6p, a homologue of the rabGDI and human choroideraemia proteins, affects cytoplasmic and mitochondrial functions

Abstract

MRS6 is a newly-identified gene in the yeast Saccharomyces cerevisiae. Its product Mrs6p shows significant homology to the mammalian GDP dissociation inhibitor (GDI) of Rab/Ypt-type small G proteins and to the human choroideraemia protein (CHM), the component A of Rab-specific GGTase II. The interaction of Mrs6p with G proteins is indicated by our observation that the MRS6 gene suppresses the effect of a temperature-sensitive ypt1 mutation. Disruption of the MRS6 gene is lethal to haploid yeast cells. This is consistent with the notion that Mrs6p is interacting with Rab/Ypt-type small G proteins, which are known to have essential functions in vesicular transport. Unexpectedly, the MRS6 gene product also affects mitochondrial functions as revealed by the facts that high-copy numbers of MRS6 (1) suppress the pet- phenotype of mrs2-1 mutant strains and (2) cause a weak pet- phenotype in wild-type strains. We conclude from these results that the MRS6 gene product has a vital function in connection with Rab/Ypt-type proteins in the cytoplasm and, in addition, affects mitochondrial functions.

Structure, regulation and cellular functions of Rab geranylgeranyl transferase and its cellular partner Rab Escort Protein

“…Binding 156 of GGPP causes minor changes in the structure, 157 mostly in the hydrophobic pocket. The region of 158 binding of the phosphate group and carbons 1-12 159 is very similar to GGT I but the bottom of the cavity is 160 expanded, which makes RGGT more tolerant to the 161 substitution of the distal part of the isoprenoid chain 162 than other CAAX prenyltransferases (Nguyen et al 163 2009(Nguyen et al 163 , 2010 (Waldherr et al 1993, Ragnini et al 1994 (Rasteiro and Pereira-Leal 2007). These inserts are 213 not similar to any other protein, in the crystal structure 214 of the rat enzyme they show no clear electron density 215 (Rak et al 2004).…”

“…mrs6 overex-859 pression caused a decrease in cell size on non-860 fermentable carbon sources (Ragnini et al 1994) but 861 depletion caused an increase in cell size in poor nutri-862 ents (Singh and Tyers 2009). An opposite effect should 863 have been expected from a simple secretory system 864 perturbation.…”

“…Microscopic obser-867 vations of spores from a heterozygous mrs6 strain 868 (completely lacking one copy of the gene) show 2:2 869 segregation, the lethality was ascribed to the fact that 870 spores either did not germinate or underwent not more 871 than three cell divisions. A conditional mutant was 872 lethal under non-permissive conditions, so the gene is 873 important for both vegetative growth and germination 874 (Ragnini et al 1994). Overexpression of the mrs6 875 protein can suppress the thermosensitive phenotype 876 of the ypt N121I/A161V mutant but not the absence of 877 ypt1 protein (Ragnini et al 1994).…”

“…A conditional mutant was 872 lethal under non-permissive conditions, so the gene is 873 important for both vegetative growth and germination 874 (Ragnini et al 1994). Overexpression of the mrs6 875 protein can suppress the thermosensitive phenotype 876 of the ypt N121I/A161V mutant but not the absence of 877 ypt1 protein (Ragnini et al 1994). Mutational analysis 878 of mrs6p led to the conclusions that mrs6p with 879 deletions in the non-conserved C-terminal amino 880 acid stretch or mutations in all but the first SCR 881 were able to rescue the mrs6 -/-conditional phenotype 882 (Bauer et al 1996).…”

The Yeast Rab Escort Protein Binds Intracellular Membranes in Vivo and in Vitro

“…REP-1 in humans is encoded by the choroideremia gene, and deletions in this gene cause a progressive retinal dystrophy leading to blindness (5,6). The yeast REP is encoded by the MRS6/MSI4 gene, which is essential for viability and Rab GGTase activity in yeast (7)(8)(9)(10). Both human and yeast REPs share structurally conserved regions with RabGDI, a protein that recognizes prenylated GDP-bound Rabs and takes part in their membrane-cytosol recycling (11)(12)(13).…”