Viral Infection of a Gram-positive Bacterium : Molecular and Cell Biology Mechanisms

Orateur : Paolo TAVARES (Unité de Virologie Moléculaire et Structurale, CNRS UPR3296, Gif sur Yvette)

Many icosahedral viruses use a specialized portal vertex for genome encapsidation and release from the viral capsid. In tailed bacteriophages this vertex is linked by a connector structure to the tail. The tail is the device that ensures specific recognition of the host bacterium and efficient transfer of the genome from the viral capsid to the bacterial cytoplasm. This architecture of the virus particle is found in more than 95 % of known bacteriophages revealing that it was retained throughout evolution as the most efficient machine to infect and kill bacterial cells. Studies of the tailed bacteriophage SPP1 viral particle before and after DNA release provide molecular details on the sequential program of structural rearrangements initiated by interaction of SPP1 with its host receptor YueB. YueB binding to the SPP1 tail fiber triggers a conformational change in the phage major tail protein subunits that is propagated as a domino-like cascade along the 160 nm-long helical tail tube to promote opening of the SPP1 capsid portal channel. DNA release is accompanied by opening and re-closure of the connector gp16 stopper and emptying of the long non-contractile tail tube. SPP1 binds preferentially to the poles of its Gram-positive host Bacillus subtilis. Polar entry of the viral genome correlates with assembly of SPP1 DNA replication foci in the bacterial cytoplasm where SPP1 replication proteins localize and rapidly recruit components of the host replisome. The molecular and cellular mechanisms supporting transfer of DNA from the virion to the host cell and the subsequent assembly of virus replication factories will be discussed.

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