Shy1p is necessary for full expression of mitochondrial COX1 in the yeast model of Leigh's syndrome

Abstract

SHY1 codes for a mitochondrial protein required for full expression of cytochrome oxidase (COX) in Saccharomyces cerevisiae. Mutations in the homologous human gene (SURF1) have been reported to cause Leigh's syndrome, a neurological disease associated with COX deficiency. The function of Shy1p/Surf1p is poorly understood. Here we have characterized revertants of shy1 null mutants carrying extragenic nuclear suppressor mutations. The steady-state levels of COX in the revertants is increased by a factor of 4-5, accounting for their ability to respire and grow on non-fermentable carbon sources at nearly wild-type rates. The suppressor mutations are in MSS51, a gene previously implicated in processing and translation of the COX1 transcript for subunit 1 (Cox1) of COX. The function of Shy1p and the mechanism of suppression of shy1 mutants were examined by comparing the rates of synthesis and turnover of the mitochondrial translation products in wild-type, mutant and revertant cells. We propose that Shy1p promotes the formation of an assembly intermediate in which Cox1 is one of the partners.

Aberrant Translation of CytochromecOxidase Subunit 1 mRNA Species in the Absence of Mss51p in the YeastSaccharomyces cerevisiae

“…No synthesis of Cox1p or the novel protein was seen in the cox1 mutant either in the presence or absence of the mss51 null mutation ( Figure 1B). These data constitute strong evidence (Barrientos et al, 2002b). (B) A partial deletion of COX1 blocks in vivo synthesis of mp15.…”

“…Mitochondrial gene products were labeled with [ 35 S]methionine (7 mCi/ mmol; GE Healthcare, Little Chalfont, Buckinghamshire, United Kingdom) in whole cells at 30°C in the presence of cycloheximide (Barrientos et al, 2002b). Equivalent amounts of total cellular proteins were separated by SDS-PAGE on a 17.5% polyacrylamide gel, transferred to a nitrocellulose membrane, and exposed to a Kodak X-OMAT x-ray film.…”

“…Mss51p was proposed to play a role in adjusting translation of Cox1p to the availability of its partners subunits during assembly of COX (Barrientos et al, 2002b. This was based on observations that synthesis of Cox1p is greatly reduced in most COX assembly mutants Figure 3, A and B).…”

“…Translation of COX1 in S. cerevisiae is under the control of the MSS51 and PET309 gene products that are also involved in maturation of the COX1 mRNAs (Decoster et al, 1990;Manthey and McEwen, 1995). Mutations in MSS51 or overexpression of the wild type gene can suppress shy1 null mutants by enhancing synthesis of Cox1p (Barrientos et al, 2002b). The function of Shy1p in maturation and/or assembly of Cox1p (Barrientos et al, 2002b;Perez-Martinez et al, 2003;Smith et al, 2005) is of considerable interest because mutations in its human homologue, Surf1p, are responsible for most diagnosed cases of Leigh's syndrome presenting a COX deficiency (Tiranti et al, 1998;Zhu et al, 1998).…”

“…Mutations in MSS51 or overexpression of the wild type gene can suppress shy1 null mutants by enhancing synthesis of Cox1p (Barrientos et al, 2002b). The function of Shy1p in maturation and/or assembly of Cox1p (Barrientos et al, 2002b;Perez-Martinez et al, 2003;Smith et al, 2005) is of considerable interest because mutations in its human homologue, Surf1p, are responsible for most diagnosed cases of Leigh's syndrome presenting a COX deficiency (Tiranti et al, 1998;Zhu et al, 1998). Cox1p synthesis is suppressed in most COX assembly mutants, including shy1 mutants, but it is restored to normal levels by mss51 suppressors of shy1 or by mutations in COX14 , which codes for a COX assembly factor (Glerum et al, 1995).…”