Intermediate Filament Formation by a Yeast Protein Essential for Organelle Inheritance

Abstract

Intermediate filaments are abundant cytoskeletal components whose specific cellular functions are poorly understood. The Saccharomyces cerevisiae protein MDM1 displays structure and solubility properties that are similar to those of intermediate filament proteins of animal cells. Yeast cells that have a mutant form of MDM1 exhibit temperature-sensitive growth and defective transfer of nuclei and mitochondria to daughter cells during incubation at the nonpermissive temperature of 37 degrees C. The purified, wild-type MDM1 protein readily forms 10-nanometer-wide filaments at either 4 degrees C or 37 degrees C. In contrast, the purified, mutant protein forms filaments at 4 degrees C but fails to form such structures at 37 degrees C. These results suggest that intermediate filament proteins are universal components of eukaryotic cells.

A High-OrderTrans-Membrane Structural Linkage Is Responsible for Mitochondrial Genome Positioning and Segregation by Flagellar Basal Bodies in Trypanosomes

“…Genes identified from mutational analysis of mitochondrial inheritance encode proteins that fall into two main groups: those likely to be associated with the cytoskeleton and those associated with the outer mitochondrial membrane (Jones and Fangman, 1992;Guan et al, 1993;Sogo and Yaffe, 1994;Berger et al, 1997;Hales and Fuller, 1997;Shepard and Yaffe, 1999;Fekkes et al, 2000). In some cases, the evidence of a cytoskeletal association points to proteins that influence mitochondrial shape and transmission to microtubules and at other times to actin microfilaments (McConnell et al, 1990;McConnell and Yaffe, 1993;Hermann et al, 1997;Otsuga et al, 1998;Sesaki and Jensen, 1999). Moreover, there is evidence that mitochondrial outer membrane proteins such as Mmm1p are also involved in processes that control the distribution and stability of the DNA nucleoid at the face of the inner mitochondrial membrane (Hobbs et al, 2001).…”

Lipid-dependent Subcellular Relocalization of the Acyl Chain Desaturase in Yeast

“…In ole1⌬ mutant cells that have been depleted of UFA, on the other hand, cellular morphology is disturbed to an extent that makes a phenotypic characterization difficult (Zhang et al, 1999). ole1 ts (mdm2) mutants after prolonged incubation at nonpermissive conditions (5.5 h), on the other hand, display collapsed mitochondria and aberrant cytosolic membrane profiles (McConnell et al, 1990).…”

“…Mutations in OLE1 have been isolated during the late 1960s in screens for oleic acid auxotrophic mutants (Resnick and Mortimer, 1966). More recently, conditional temperature-sensitive (ts) mutations of OLE1 have been isolated in screens for mutants that fail to transmit mitochondria from the mother cell to the growing bud (McConnell et al, 1990;Stewart and Yaffe, 1991;Hermann et al, 1997). Analysis of one of these mutants, mdm2, revealed that reduced levels of UFAs result in a severe perturbation of cellular membranes, most notably of the nuclear envelope and of mitochondria (Stewart and Yaffe, 1991;Schneiter and Kohlwein, 1997;Zhang et al, 1999).…”

Mitochondrial transmission during mating in Saccharomyces cerevisiae is determined by mitochondrial fusion and fission and the intramitochondrial segregation of mitochondrial DNA.

“…A yeast cell contains from 1 to 10 mitochondria that form reticular structures localized at the cortex of the cell (Hoffman and Avers, 1973;Stevens, 1979Stevens, , 1981. Segregation of yeast mitochondria occurs at a specific point in the cell cycle, when a portion of the mitochondrial reticulum moves into the emerging daughter bud (Stevens, 1981;McConnell et al, 1990). The cortical localization and reticular structure of mitochondria are important for their inheritance because mutants with abnormal mitochondrial morphology fail to distribute mitochondria into daughter cells (McConnell et al, 1990).…”

“…Segregation of yeast mitochondria occurs at a specific point in the cell cycle, when a portion of the mitochondrial reticulum moves into the emerging daughter bud (Stevens, 1981;McConnell et al, 1990). The cortical localization and reticular structure of mitochondria are important for their inheritance because mutants with abnormal mitochondrial morphology fail to distribute mitochondria into daughter cells (McConnell et al, 1990). To date, the analysis of these mutants suggests that normal morphology requires specific mitochondrial outer membrane proteins and a protein homologous to the mammalian intermediate filament protein vimentin Yaffe, 1992, 1993;Burgess et al, 1994;Sogo and Yaffe, 1994).…”