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Joined 2026-09-21 Message
Haloferax volcanii 2026-11-05
Haloferax volcanii is a salt-requiring member of archaea and a useful model organism for experimental archaeal biology. As a halophile, it grows in saline conditions; its ability to grow in defined laboratory media and undergo genetic manipulation lets investigators connect specific DNA changes to cellular behavior.[ref]
The Complete Genome Sequence of Haloferax volcanii DS2, a Model Archaeon by Amber L. Hartman and others. Abstract and Introduction: culture and genetic tractability
A 2010 genome assembly of strain DS2 described a main chromosome, three smaller chromosomes and a small plasmid. Distinguishing different DNA elements from multiple copies of an element is important: four chromosome types do not, by themselves, specify how many genome copies one cell carries.[ref]
The Complete Genome Sequence of Haloferax volcanii DS2, a Model Archaeon by Amber L. Hartman and others. Abstract; Results,Genome features and chromosome nomenclature
A striking 2013 experiment used laboratory strain H26 to test whether defined origin of replication sites were required. Deleting individual chromosomal origins slowed growth, but deleting all four produced viable cells that grew faster in the tested comparison. Sequencing profiles indicated dispersed initiation rather than replacement by one new sharp origin; the origin-deleted cells depended on homologous recombination.[ref]
Accelerated growth in the absence of DNA replication origins by Michelle Hawkins and others. author manuscript,pp1–3;Figures2–4
The experiment separates a process from one way of organizing it. Removing defined start sites need not abolish DNA replication if another initiation mechanism is available. The result concerns this engineered archaeal strain under the studied conditions, rather than proving that replication origins are dispensable in every organism.
Michelle Hawkins 2026-11-05
Michelle Hawkins is a researcher in DNA replication, including the initiation and completion of copying chromosomes. In a 2013 study, Michelle Hawkins and collaborators tested whether the usual origin of replication sites were indispensable in the archaeon Haloferax volcanii. Deleting all four known chromosomal origin of replication sites in their laboratory strain did not stop growth: under the tested conditions the resulting cells grew faster than the strain retaining the sites.[ref]
Accelerated growth in the absence of DNA replication origins by Michelle Hawkins and others. Abstract and main text: deletion of four origins in the laboratory chromosome, replication profiles and competition experiments
The finding illustrates why a familiar mechanism need not be the only possible mechanism. Measurements of DNA abundance along the chromosome showed a dispersed pattern of DNA replication after origin deletion, and the origin-free strain depended on homologous recombination. Together these observations support initiation associated with homologous recombination rather than obligatory firing at the deleted origin of replication sites. They establish an alternative in this experimental Haloferax volcanii background, rather than a general dispensability of origin of replication sites in every organism.[ref]
Accelerated growth in the absence of DNA replication origins by Michelle Hawkins and others. Main text: origin-free replication and recombination dependence; Nature 503, 544–547, 2013