Investigating the roles of MSS51 in translation activation of COX1 and assembly of Cox1p into cytochrome c oxidase.

摘要

The S. cerevisiae the nuclear gene MSS51 is required for synthesis of mitochondrially encoded Cox1. the largest subunit of cytochrome c oxidase. MSS51 functionally interacts with the 5'-untranslated region (UTR) of COX1 mRNA to activate translation, and also physically interacts with newly synthesized Cox1p as a component of early assembly intermediates. These dual functions of Mss5l couple Cox1 synthesis to assembly of cytochrome c oxidase. Mss51 has no previously described amino acid sequence domains or motifs.;Two partial separation-of-function mss51 alleles were obtained by screening for mutations that allow expression of the ARG8m reporter inserted in place of the COX1 coding sequence between the COX1 UTRs. but not the COX1 coding sequence flanked by UTRs from the COX2 mRNA. One. mss51-W64R, also fails to express COX1 from its native locus. Thus. mss51-W64R activates translation at the COX1 5' UTR, but has a defect in downstream assembly steps of Cox1. When overexpressed, mss51-W64R was able to promote respiratory growth. indicating that mss51-W64R is not completely deficient in assembly functions. I therefore propose that the single missense mutation of mss51-W64R is integral in its role of formation of the Cox1 assembly complex.;A second allele identified in the screen. mss51-102, allows only weak respiratory growth when COX1 is flanked by COX2 UTRs. but strong respiratory growth when COX1 5' UTR is present in cis to the COX1 coding sequence. I selected for spontaneous mutants that enhanced the weak respiration in a strain with mss51-102 bearing cox2::COX1 cox1::ARG8m mtDNA. I identified a novel mitochondrial rearrangement resulting from the apparent duplication of the COX1 5' leader. causing it to be present at both COX1 and ARG8m. I propose that the strong preference of mss51-102 for the COX1 5' leader to be present in cis to the coding sequence implies that the same Mss51lp molecule that activates translation is transferred in cis to the nascent Cox1 peptide.