Large-scale Effectors of Gene Expression and New Models of Cell Division in the Haloarchaea.
Like most Archaea, the hypersaline-adapted organism Halobacterium salinarum exhibits characteristics from all three domains of life, including a eukaryotic histone protein, a universal propensity to genetic rearrangements, and homologs of bacterial cell division proteins. Here we investigate the ancestral function of histone protein in the Archaea. Transcriptomics, proteomics, and phenotypic assays of histone mutants determine that histone regulates gene expression and cell shape but not genome compaction in H. salinarum. We further explore the regulation of gene expression on a genome-wide scale through the study of genomic instability. Genomic deletions and duplications are detected through the meta-analysis of 1154 previously published gene expression arrays and 48 chromatin immunoprecipitation arrays. We discover that a 90 kb duplication event in the megaplasmid pNRC100 directly leads to increased gene expression, and find evidence that the chromosome is far more unstable than previously assumed. These events are all linked with the presence of mobile insertion elements. Finally, in response to questions generated by these experiments, we develop a novel time-lapse protocol for H. salinarum and ask basic questions about single cell dynamics during division. Fluorescent labeling of homologs to bacterial cell division proteins confirms their involvement in cell division but localization dynamics contradict the basic bacterial model. The discovery of unusual facets of morphology during cell division is consistent with these novel protein dynamics and opens up new avenues of inquiry into archaeal cell division.
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