Dogma-defying bacteria package DNA in unusual ways

A startling discovery in micro organism means that some species have an odd means of packing chromosomes and regulating gene expression — utilizing proteins that, till just lately, weren’t regarded as current in micro organism in any respect.

In a preliminary model posted to bioRxiv on January 26, the researchers report the characterization of proteins known as histones that seem to hyperlink collectively in two sorts of micro organism to span areas of the bacterial chromosome.¹. That is fairly completely different from the association of histones seen in different organisms. For instance, in organisms known as eukaryotes, whose cells have a membrane-enclosed nucleus, DNA wraps round histones, reasonably than being enveloped by them.

Though histones are very important instruments for sustaining chromosome construction and controlling gene exercise in eukaryotes and microorganisms known as archaea, it was extensively assumed for years that they don’t exist in micro organism.

As extra bacterial genome sequences grew to become out there, the invention of distinct sequences of histones challenged this assumption². “However nobody has characterised it or executed purposeful research,” says Remus Dam, a biochemist and microbiologist at Leiden College within the Netherlands. “That is positively one thing new and attention-grabbing.”

unified construction

Eukaryotic histones are remarkably uniform of their construction and performance—a consistency that may be irritating for researchers who need to examine histone evolution, says College of Colorado Boulder biochemist Caroline Luger. “If you wish to get to the evolutionary origin, you may’t go to ‘primitive’ eukaryotes,” she says. “They have already got the whole lot.”

The shortage of range additionally raises questions for artificial biologists in search of new methods to manage gene expression, says Tobias Warnecke, a molecular evolutionary biologist at Imperial Faculty London. “The fundamental construction of chromatin and the way gene expression works may be very comparable throughout eukaryotes,” he says, “and you then begin to marvel, ‘Is that this a freezing accident? “Is there one thing particular about histones that makes them distinctive, or can we construct techniques another way?”

Latest explorations of primitive histones have yielded extra various techniques, and Warnecke and Antoine Hucher, a techniques biologist additionally at Imperial, determined to see what surprises bacterial histone-like proteins would possibly maintain. Along with Luger and different collaborators, they examine proteins of two species that may be simply grown within the laboratory: the pathogen Leptospira interrogans They’re known as predatory micro organism Bdellovibrio is bacterial. This infiltrates bigger micro organism and digests them from the within, chopping up the DNA and proteins of their prey to make use of as constructing blocks to copy themselves.

When the researchers remoted the histone protein from bacteriophorus They analyzed its construction, each by itself and whereas interacting with DNA, and had been stunned to seek out that it didn’t behave like every recognized histones from archaea or eukaryotes. Bacterial histones are grouped collectively in pairs surrounding the DNA strand. Lengthy chains of those can act as a protect across the DNA, a notable distinction from their operate in eukaryotes, the place histones mixture collectively to type a spool round which the DNA winds. “I used to be blown away,” says Luger.

protecting proteins

It is a startling discovering, nevertheless it’s nonetheless not clear if this construction displays how histones and DNA work together in bacterial cells, or if it is the results of working with remoted proteins within the lab, Dam says.

For now, researchers can solely speculate about what histones could be doing, and the way their uncommon mode of motion would possibly assist micro organism survive. to B. bacterialHistones can shield DNA from choosing up stray items from the fragmented genomes of their prey, Warnick says.

Micro organism are additionally recognized to include tightly compressed DNA throughout their free-swimming section, earlier than they infect their prey, notes Geraldine Laloux, a microbiologist at Université Catholique de Louvain in Belgium. “We have been questioning what drives this very robust stress and the way does it go away,” says Laloux. “This distinctive means of splicing DNA can convey new insights into this matter.”

As a part of their examine, the researchers scanned 1000’s of bacterial genomes. They discovered histone-like proteins in about 2% of genomes, suggesting that there shall be many different techniques to check. “Folks obtained excited and mentioned, ‘Micro organism weren’t presupposed to have histones,'” Warnick says. “However for those who’re engaged on microbial evolution, you realize for those who look onerous sufficient, you will discover some.”