Fungus fights malaria? - The Scientist - Magazine of the Life Sciences

Fungus fights malaria? - The Scientist - Magazine of the Life Sciences

A Promiscuous DNA Packaging Machine from Bacteriophage T4

Complex viruses are assembled from simple protein subunits by sequential and irreversible assembly. During genome packaging in bacteriophages, a powerful molecular motor assembles at the special portal vertex of an empty prohead to initiate packaging. The capsid expands after about 10%–25% of the genome is packaged. When the head is full, the motor cuts the concatemeric DNA and dissociates from the head. Conformational changes, particularly in the portal, are thought to drive these sequential transitions. We found that the phage T4 packaging machine is highly promiscuous, translocating DNA into finished phage heads as well as into proheads. Optical tweezers experiments show that single motors can force exogenous DNA into phage heads at the same rate as into proheads. Single molecule fluorescence measurements demonstrate that phage heads undergo repeated initiations, packaging multiple DNA molecules into the same head. These results suggest that the phage DNA packaging machine has unusual conformational plasticity, powering DNA into an apparently passive capsid receptacle, including the highly stable virus shell, until it is full. These features probably led to the evolution of viral genomes that fit capsid volume, a strikingly common phenomenon in double-stranded DNA viruses, and will potentially allow design of a novel class of nanocapsid delivery vehicles.

enlace al artículo

Nature (nº especial)The Human Genome at Ten .

The Human Genome at Ten

The draft human genome sequence was published on February 15 2001. Its publication promised great insights into human biology, medicine and evolution; it also changed the way life science research was done. In this special, Nature reflects on the past ten years to take stock of what we have learnt about the genome itself and about us - our biology, evolution and the genetic basis of human disease. From today's standpoint we also look into the future of human genomics, with a special focus on its role in clinical medicine.

Jaime Pellicer y el mayor genoma secuenciado

Jaume and the Giant Genome

Japanese canopy plant (Paris japonica)

He found that the canopy plant genome had 150 billion base pairs—50 times as many as human DNA. If the DNA in a human cell were unraveled, it would stretch to two meters. A strand of DNA in the canopy plant would span 100 meters. 

In fact, in humans, only about 1.5 percent of the genome’s DNA codes for proteins. In the Japanese canopy plant the percentage is sure to be even less. The function of that surplus DNA—or even whether there is a function—is a hotly debated mystery and will likely remain so until the species is sequenced. 

Noncoding sequences used to go by the derogatory names “selfish” or “junk” DNA, but have more recently acquired milder tags, including “transposable elements” or “jumping genes.” Unless somehow restrained, these proliferate across genomes like weeds. One sequence, called Alu, has copied itself a million times and makes up some 10 percent of the human genome.

There is, however, some evidence that the canopy plant, despite—or perhaps because of—its huge genome, maintains a competitive edge over plants that share its mountain habitat. In the chilly months of early spring, while neighboring competitors sit dormant, and before overhead trees come into leaf, the plant gets a jump-start on growth by pumping its cells full of water. This cellular expansion allows the canopy plant to increase its size and soak up more sunlight before DNA replication and cell division occur in the warmer summer months.


Read more: Jaume and the Giant Genome - The Scientist - Magazine of the Life Sciences http://www.the-scientist.com/article/display/57932/#ixzz1DOJgSbet