Gag3p, an outer membrane protein required for fission of mitochondrial tubules

Area of Science:

• Cell Biology
• Mitochondrial Dynamics
• Genetics

Background:

• Mitochondrial morphology and function are regulated by the MGM1 gene, which encodes a dynamin-like protein on the mitochondrial outer membrane.
• Mitochondrial fragmentation and genome loss can result from MGM1 gene lesions.

Purpose of the Study:

• To identify and characterize novel mutations that suppress mitochondrial fragmentation and genome loss caused by MGM1 lesions.
• To elucidate the roles of these novel genes in mitochondrial fission and morphology.

Main Methods:

• Genetic screening for suppressor mutations (gag1, gag2, gag3) in Saccharomyces cerevisiae.
• Analysis of mitochondrial morphology using microscopy.
• Genetic mapping of mutations.
• Subcellular localization studies of proteins.

Main Results:

• Three novel mutations, gag1, gag2, and gag3, were identified that suppress mitochondrial fragmentation and genome loss associated with MGM1 defects.
• Cells with gag mutations exhibit aberrant mitochondrial morphology with elongated, unbranched tubules and fenestrated structures.
• The gag1 mutation maps to DNM1, a gene essential for mitochondrial fission.
• GAG3 encodes a novel WD40-repeat protein (Gag3p) localized to the outer mitochondrial membrane, which associates peripherally and plays a distinct role in mediating mitochondrial tubule fission.
• Gag3p localization is independent of Dnm1p and Gag2p, but Gag2p is required for Dnm1p localization to the mitochondrial outer membrane.

Conclusions:

• The gag mutations identify new components involved in the regulation of mitochondrial fission.
• Gag3p is a novel mitochondrial outer membrane protein that functions in mitochondrial tubule fission.
• Gag2p plays a role in the localization of Dnm1p, a key protein in mitochondrial fission.