DNA translocase

Fig. 2. Homology of chromatin remodeling ATPases to DNA translocases. Motifs I-III, V, and VI in the Sf2 helicase signature in the Swi/Snf superfamily (including yeast Motlp, Radl6p and Rad54p) are aligned and compared with the motifs in reverse gyrase Sf2-like signature and the PerA helicase Sfl signature. The conserved elements of the latter two are taken from Refs. [192] and [333], respectively.

Fig. 3. Topological coupling of DNA translocation and chromatin remodeling. (A) Alternative models for remodeling of a single nucleosome driven by the translocating complexes are compared with passive remodeling driven by the SP6 RNA polymerase or RNA polymerase III [109]. Note that no superhelicity would be constrained unless rotation of the translocase and DNA ends is impeded or prevented. It is also assumed that translocation occurs in steps of less than 5bp. CRA, chromatin remodelling assembly. The arrows indicate the direction of translocation of the DNA. (B) Model for remodeling of a nucleosome array within a topologically defined domain. Adapted with permission from Ref [119].

If the torsional strain generated by DNA translocation is utilized for mobilizing nucleosomes [195] then the direction of translocation will play an important role in determining the direction in which DNA is passed over the nucleosome surface and the orientation in which torsion is altered. Provided that rotation of the remodeling complex is restricted, incremental translocation of the motor towards the nucleosome will apply positive superhelical torsion to the particle whereas translocation away the nucleosome will apply negative superhelical torsion [119] (Fig. 3). The problem then is how to translate the motion of the translocase into translational... 

Genetic mutations also have been reported for mitochondrial proteins encoded by nuclear DNA. Most of the estimated 1,000 proteins required for oxidative phosphorylation are encoded by nuclear DNA, whereas mtDNA encodes only 13 subunits of the oxidative phosphorylation complexes (including ATP synthase). Nuclear DNA encodes the additional 70 or more subunits of the oxidative phosphorylation complexes, as well as adenine nucleotide translocase (ANT) and other anion translocators. Coordinate regulation of expression of nuclear and mtDNA, import of proteins into the mitochondria, assembly of the complexes, and regulation of mitochondrial fission are nuclear encoded. 

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