Translational Regulation of Nuclear Gene COX4 Expression by Mitochondrial Content of Phosphatidylglycerol and Cardiolipin in Saccharomyces cerevisiae

Abstract

Previous results indicated that translation of four mitochondrion-encoded genes and one nucleus-encoded gene (COX4) is repressed in mutants (pgs1⌬) of Saccharomyces cerevisiae lacking phosphatidylglycerol and cardiolipin. COX4 translation was studied here using a mitochondrially targeted green fluorescence protein (mtGFP) fused to the COX4 promoter and its 5 and 3 untranslated regions (UTRs). Lack of mtGFP expression independent of carbon source and strain background was established to be at the translational level. The translational defect was not due to deficiency of mitochondrial respiratory function but was rather caused directly by the lack of phosphatidylglycerol and cardiolipin in mitochondrial membranes. Reintroduction of a functional PGS1 gene under control of the ADH1 promoter restored phosphatidylglycerol synthesis and expression of mtGFP. Deletion analysis of the 5 UTR COX4 revealed the presence of a 50-nucleotide fragment with two stem-loops as a cis-element inhibiting COX4 translation. Binding of a protein factor(s) specifically to this sequence was observed with cytoplasm from pgs1⌬ but not PGS1 cells. Using HIS3 and lacZ as reporters, extragenic spontaneous recessive mutations that allowed expression of His3p and ␤-galactosidase were isolated, which appeared to be loss-of-function mutations, suggesting that the genes mutated may encode the trans factors that bind to the cis element in pgs1⌬ cells.

An essential bacterial-type cardiolipin synthase mediates cardiolipin formation in a eukaryote

“…This interpretation is consistent with previous studies showing that CL is necessary for proper function and stability of several mitochondrial proteins and protein complexes (19,51). Alternatively, it is possible that depletion of CL may affect mitochondrial protein levels in T. brucei by downregulating translation of complex proteins, as has been shown for Cox4 translation in a yeast mutant lacking PG and CL (52).…”

Involvement of cytochrome c oxidase subunits Va and Vb in the regulation of cancer cell metabolism by Bcl-2

“…Furthermore, the yeast analog of COX Vb, COX IV, has been shown to be post-transcriptionally regulated by the cardiolipin content of the mitochondria. 27 The likelihood of Bcl-2 affecting COX Vb localization to the outer mitochondrial membrane is ruled out, as total COX Vb from the intact mitochondria fraction is the same in CEM/Neo and Bcl-2 cells, suggesting that Bcl-2-mediated COX Vb translocation across mitochondrial membranes may be linked to the enhanced localization of COX Va. One possible explanation would be that COX assembly is a multistep process and COX Va is upstream of COX Vb in the assembly hierarchy; increased COX Va-assembled intermediates may promote the downstream incorporation of COX Vb, which has been harboring at the outer mitochondrial membrane, waiting for translocation into the inner mitochondrial membrane to form COX. Alternatively, Bcl-2 and the yeast homolog COX IV (COX Vb) have also been shown to interact with mitochondrial import protein Tom20 in Saccharomyces cerevisiae, an implication that Bcl-2 may similarly promote the import of COX Vb across mitochondrial membranes through Tom20 in the mammalian system.…”

Deletion of the Cardiolipin-specific Phospholipase Cld1 Rescues Growth and Life Span Defects in the Tafazzin Mutant

“…Furthermore, overexpression of components of the Hap2/3/4/5p complex rescues cytochrome c oxidase deficiencies (79). In another example of coordinate control, regulation of COX4 translation requires Pgs1, the enzyme that catalyzes the committed step of CL synthesis (80). Taken together these findings suggest an integrated and concerted response to environmental stress that affects the CL pathway and oxidative phosphorylation, both of which are interconnected.…”