Nucleoid localization of Hsp40 Mdj1 is important for its function in maintenance of mitochondrial DNA

Document Type

Article

Publication Date

10-1-2013

Subject Area

Cell Nucleus (genetics, metabolism); DNA Replication; DNA, Mitochondrial (genetics); HSP40 Heat-Shock Proteins (genetics, metabolism); HSP70 Heat-Shock Proteins (genetics, metabolism); Membrane Proteins (genetics, metabolism); Mitochondria (metabolism); Plasmids; Polymerase Chain Reaction; Saccharomyces cerevisiae (genetics, growth & development, metabolism); Saccharomyces cerevisiae Proteins (genetics, metabolism)

Abstract

Faithful replication and propagation of mitochondrial DNA (mtDNA) is critical for cellular respiration. Molecular chaperones, ubiquitous proteins involved in protein folding and remodeling of protein complexes, have been implicated in mtDNA transactions. In particular, cells lacking Mdj1, an Hsp40 co-chaperone of Hsp70 in the mitochondrial matrix, do not maintain functional mtDNA. Here we report that the great majority of Mdj1 is associated with nucleoids, DNA-protein complexes that are the functional unit of mtDNA transactions. Underscoring the importance of Hsp70 chaperone activity in the maintenance of mtDNA, an Mdj1 variant having an alteration in the Hsp70-interacting J-domain does not maintain mtDNA. However, a J-domain containing fragment expressed at the level that Mdj1 is normally present is not competent to maintain mtDNA, suggesting a function of Mdj1 beyond that carried out by its J-domain. Nevertheless, loss of mtDNA function upon Mdj1 depletion is retarded when the J-domain, is overexpressed. Analysis of Mdj1 variants revealed a correlation between nucleoid association and DNA maintenance activity, suggesting that localization is functionally important. We found that Mdj1 has DNA binding activity and that variants retaining DNA-binding activity also retained nucleoid association. Together, our results are consistent with a model in which Mdj1, tethered to the nucleoid via DNA binding, thus driving a high local concentration of the Hsp70 machinery, is important for faithful DNA maintenance and propagation.

Publication Title

Biochimica et biophysica acta

Volume

1833

Issue

10

First Page

2233

Last Page

43

Digital Object Identifier (DOI)

10.1016/j.bbamcr.2013.05.012

PubMed ID

23688635

ISSN

0006-3002

Language

eng

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