Driving Apart and Segregating Genomes in Archaea

Abstract

Genome segregation is a fundamental biological process in organisms from all domains of life. How this stage of the cell cycle unfolds in Eukarya has been clearly defined and considerable progress has been made to unravel chromosome partition in Bacteria. The picture is still elusive in Archaea. The lineages of this domain exhibit different cell-cycle lifestyles and wide-ranging chromosome copy numbers, fluctuating from 1 up to 55. This plurality of patterns suggests that a variety of mechanisms might underpin disentangling and delivery of DNA molecules to daughter cells. Here I describe recent developments in archaeal genome maintenance, including investigations of novel genome segregation machines that point to unforeseen bacterial and eukaryotic connections.

Keywords: Archaea.; chromosome; genome segregation; plasmid.

Figure 1

Ploidy in a Set of Characterized Members of the Euryarchaea and Crenarchaea Phyla. All the euryarchaeal species (green box) contain multiple chromosome copies, whereas the crenarchaeal species (blue box) harbour a single chromosome.

Figure 2

The SegAB System Is Widespread across Archaea. (A) Organization of the segAB cassette, including the upstream sso0033 gene and the two DNA sites (in lilac) to which SegB binds. (B) Phylogenetic tree of a nonexhaustive set of SegB orthologs. Genomic context studies show that each segB gene is accompanied by a segA gene. Blue box, crenarchaeal SegB cluster; green box, euryarchaeal SegB orthologs. Within the crenarchaeal cluster the Sulfolobus solfataricus P2 strain, whose SegAB have been characterized, is shown in red.

Figure 3

Organization and Structures of the pNOB8 AspA–ParBA System. (A) Schematic diagram of the gene cluster. The 3′ end of aspA overlaps with the 5′ end of parB, and the 3′ end of parB overlaps with the 5′ end of parA. (B) AspA–DNA structure (PDB 5FC0) showing three interacting AspA dimers (in orange, green, and blue) associated with the DNA fragment containing the 23 bp putative centromeric site. (C) Adenylyl-imidodiphosphate (AMP-PNP)-bound ParA dimer structure (PDB 4RU8). The ATP analog AMP-PNP is shown in red. (D) (Left) ParB-N structure (PDB 4RSF); (right) ParB-C dimer structure with one monomer shown in green and the other in magenta (PDB 4RS7). The structural images were generated by using PyMOL version 1.8.0.7 (Schrodinger) using the indicated PDB coordinates.