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Packaging of Single DNA Molecules by the Yeast Mitochondrial Protein Abf2p

Laurence R. Brewer ^*, Raymond Friddle  , Aleksandr Noy , Enoch Baldwin , Shelley S. Martin , Michele Corzett , Rod Balhorn  and Ronald J. Baskin 

^* Electronics Engineering Technologies Division, Chemistry and Materials Science Division, and Biology and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, California 94550 USA; and Department of Molecular and Cellular Biology and Graduate Group in Biophysics University of California at Davis, Davis, California 95616 USA

Correspondence: Address reprint requests to L. Brewer, E-mail: brewer1{at}llnl.gov.

Mitochondrial and nuclear DNA are packaged by proteins in a very different manner. Although protein-DNA complexes called "nucleoids" have been identified as the genetic units of mitochondrial inheritance in yeast and man, little is known about their physical structure. The yeast mitochondrial protein Abf2p was shown to be sufficient to compact linear dsDNA, without the benefit of supercoiling, using optical and atomic force microscopy single molecule techniques. The packaging of DNA by Abf2p was observed to be very weak as evidenced by a fast Abf2p off-rate (k_off = 0.014 ± 0.001 s^-1) and the extremely small forces (<0.6 pN) stabilizing the condensed protein-DNA complex. Atomic force microscopy images of individual complexes showed the 190-nm structures are loosely packaged relative to nuclear chromatin. This organization may leave mtDNA accessible for transcription and replication, while making it more vulnerable to damage.

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