Structural asymmetry and discrete nucleic acid subdomains in the Trypanosoma brucei kinetoplast

Eva Gluenz,Keith Gull,Michael K Shaw

doi:10.1111/j.1365-2958.2007.05749.x

Eva Gluenz, Keith Gull + Show 1 more

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https://doi.org/10.1111/j.1365-2958.2007.05749.x

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Journal: Molecular microbiology	Publication Date: May 18, 2007
Citations: 91	License type: cc-by

Affiliation: University of Oxford

Abstract

The mitochondrial genome of Trypanosoma brucei is contained in a specialized structure termed the kinetoplast. Kinetoplast DNA (kDNA) is organized into a concatenated network of mini and maxicircles, positioned at the base of the flagellum, to which it is physically attached. Here we have used electron microscope cytochemistry to determine structural and functional domains involved in replication and segregation of the kinetoplast. We identified two distinct subdomains within the kinetoflagellar zone (KFZ) and show that the unilateral filaments are composed of distinct inner and outer filaments. Ethanolic phosphotungstic acid (E-PTA) and EDTA regressive staining indicate that basic proteins and DNA are major constituents of the inner unilateral filaments adjoining the kDNA disc. This evidence for an intimate connection of the unilateral filaments in the KFZ with DNA provides support for models of minicircle replication involving vectorial export of free minicircles into the KFZ. Unexpectedly however, detection of DNA in the KFZ throughout the cell cycle suggests that other processes involving kDNA occur in this domain. We also describe a hitherto unrecognized, intramitochondrial, filamentous structure rich in basic proteins that links the kDNA discs during their segregation and is maintained between them for an extended period of the cell cycle.

Highlights

Kinetoplastid protozoa possess a single mitochondrion that forms an extended tubular structure and contains within it an unusually organized mitochondrial genome, segmented into thousands of circular molecules of two size classes, termed mini- and maxicircles
The mitochondrial genome of Trypanosoma brucei is contained in a specialized structure termed the kinetoplast
We identified two distinct subdomains within the kinetoflagellar zone (KFZ) and show that the unilateral filaments are composed of distinct inner and outer filaments

Summary

Introduction

Kinetoplastid protozoa possess a single mitochondrion that forms an extended tubular structure and contains within it an unusually organized mitochondrial genome, segmented into thousands of circular molecules of two size classes, termed mini- and maxicircles Maxicircles (22 kb) are present in a few dozen identical copies and contain DNA sequences that encode mitochondrial proteins, rRNA and some guide RNAs. The guide RNAs direct processing of maxicircle transcripts, which occurs by a complex process of RNA editing involving addition or deletion of uridine nucleotides (Benne et al, 1986; Stuart et al, 2005). Minicircles (1 kb), which encode the majority of guide RNAs are present in thousands of copies and heterogeneous in sequence. Accurate replication of this complex concatenated network of kinetoplast DNA (kDNA), and continuous faithful inheritance of a full complement of mini- and maxicircles to daughter cells requires specialized mechanisms that are still unclear (Liu et al, 2005)

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