Limits...
Driving Apart and Segregating Genomes in Archaea

View Article: PubMed Central - PubMed

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.

No MeSH data available.


Related in: MedlinePlus

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.
© Copyright Policy - CC BY
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5120986&req=5

fig0010: 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.

Mentions: A recent study has reported the identification and initial characterization of a dedicated chromosome-segregation system in the thermophilic crenarchaeon S. solfataricus[50]. This genome-partitioning apparatus consists of two proteins, SegA and SegB, and a cis-acting centromere-like region (Figure 2A). Intriguingly, the complex is a hybrid partition machine: SegA is an ortholog of bacterial, Walker-type chromosome-encoded ParA proteins, whereas SegB is an archaea-specific factor lacking any sequence identity to either eukaryotic or bacterial proteins. However, SegB displays sequence identity to a group of conserved, uncharacterized proteins present in both Crenarchaea (∼80% identity) and some Euryarchaea (30–46% identity) (Figure 2B). Interestingly, the genes encoding SegB proteins are located invariably downstream of segA orthologs. BLAST searches against archaeal genomes available so far indicated that the segAB cassette is present in an array of archaeal genera belonging to both Crenarchaea and Euryarchaea phyla (Figure 2B). Although the ploidy and genome content has not been determined for all these genera, what is tantalizing is that the majority of these Archaea are monoploid, or at most diploid such as M. thermautotrophicus. If a cell harbours only one or two copies of the chromosome, then a rigorous toolkit to segregate DNA at cell division is a stringent sine qua non. The 3′ end of segA overlaps with the 5′ end of segB: this arrangement suggests that the genes may be part of a single transcriptional unit implying that SegA and SegB work together to effect the same biological process. Supporting evidence derives from a transcription profiling study showing that the Sulfolobus acidocaldarius homologues of segA and segB are coexpressed in a cell-cycle-regulated fashion [51].


Driving Apart and Segregating Genomes in Archaea
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.
© Copyright Policy - CC BY
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120986&req=5

fig0010: 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.
Mentions: A recent study has reported the identification and initial characterization of a dedicated chromosome-segregation system in the thermophilic crenarchaeon S. solfataricus[50]. This genome-partitioning apparatus consists of two proteins, SegA and SegB, and a cis-acting centromere-like region (Figure 2A). Intriguingly, the complex is a hybrid partition machine: SegA is an ortholog of bacterial, Walker-type chromosome-encoded ParA proteins, whereas SegB is an archaea-specific factor lacking any sequence identity to either eukaryotic or bacterial proteins. However, SegB displays sequence identity to a group of conserved, uncharacterized proteins present in both Crenarchaea (∼80% identity) and some Euryarchaea (30–46% identity) (Figure 2B). Interestingly, the genes encoding SegB proteins are located invariably downstream of segA orthologs. BLAST searches against archaeal genomes available so far indicated that the segAB cassette is present in an array of archaeal genera belonging to both Crenarchaea and Euryarchaea phyla (Figure 2B). Although the ploidy and genome content has not been determined for all these genera, what is tantalizing is that the majority of these Archaea are monoploid, or at most diploid such as M. thermautotrophicus. If a cell harbours only one or two copies of the chromosome, then a rigorous toolkit to segregate DNA at cell division is a stringent sine qua non. The 3′ end of segA overlaps with the 5′ end of segB: this arrangement suggests that the genes may be part of a single transcriptional unit implying that SegA and SegB work together to effect the same biological process. Supporting evidence derives from a transcription profiling study showing that the Sulfolobus acidocaldarius homologues of segA and segB are coexpressed in a cell-cycle-regulated fashion [51].

View Article: PubMed Central - PubMed

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.

No MeSH data available.


Related in: MedlinePlus