New Protein Pmn34 with an Exonuclease Motif Localizes in the Mitochondrial Nucleoid Periphery of Physarum polycephalum

Abstract

Summary Mitochondrial DNA (mtDNA) is highly organized into a compact structure, the mitochondrial nucleoid (mt-nucleoid). To facilitate our understanding of the regulation of mtDNA genetic activity within the mt-nucleoid structure, we have identified a novel mt-nucleoid protein Pmn34 (Physarum polycephalum mitochondrial nucleoid protein 34), having a molecular weight of 34 kDa, from pure mt-nucleoids isolated from the true slime mold, Physarum polycephalum. The Pmn34 protein is composed of 326 amino acids with mitochondrial transit peptides and its primary sequence contains a conserved 3Ј to 5Ј exonuclease motif of the "DEDD" superfamily. DNA mobility shift assays demonstrated that recombinant Pmn34 binds weakly to both mtDNA and lDNA with no apparent sequence specificity. Furthermore, immunoblotting and immunostaining analyses revealed that Pmn34 localizes specifically in the peripheral region of mt-nucleoids. These results indicate that Pmn34 functions in the peripheral region of mt-nucleoids, suggesting that the mt-nucleoid is compartmentalized into functional domains.

Smooth Loop-Like Mitochondrial Nucleus in the Primitive Red Alga <i>Cyanidioschyzon merolae</i> Revealed by Drying Treatment

“…Although the DNA content per mitochondrion decreased remarkably with spherulation and the mt-nucleus became short, the mt-nuclei were smooth. Similar images were recorded for isolated mt-nuclei of P. polycephalum (Sasaki et al 1998, Itoh et al 2009. On the basis of these results, we suggest that mtDNA molecules assemble smooth loop-shaped mitochondrial nuclei by a mechanism that is conserved in various eukaryotes.…”

“…Multiple copies of mtDNA are organized by DNA binding proteins in various organisms including yeast (Miyakawa et al 1987, Miyakawa 2017, slime molds (Sasaki et al 1998, Itoh et al 2009, algae, and plants (Sakai et al 2004, Kobayashi et al 2017, and animals (Satoh and Kuroiwa 1991). However, despite extensive research toward the genetic or proteomic identification of the DNA binding proteins, such as Grom and HU-like proteins (Sasaki et al 1998, Kobayashi et al 2002, Itoh et al 2009, it is not clear how mtDNA copies are organized morphologically. The red alga C. merolae diverged early in eukaryotic evolution (Frederick and Seckbach 1986).…”

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“…)． その後オルガネラ核の研究は核を構 成するタンパク質の同定など大きく発展した (Kobayashi et al 2002, Sasaki et al 2003, Sakai et al 2004, Itoh et al 2010 (Nakamura et al 1988(Nakamura et al , 1989(Nakamura et al , 1991 (Kawano et al1993, Takano et al 1996, 1997 (Nagata et al 1999a(Nagata et al , 1999b(Nagata et al , 2010． そし て以前われわれの研究室にいた北京大学の蘇都莫日 根さんのグループによって片親遺伝の分子機構が分子 細胞学的に証明された (Sodmergen 1992(Sodmergen , 1994(Sodmergen , 1995(Sodmergen , 2010…”