Microbiology. Action at a distance--bacterial flagellar assembly

The rotating motion of a helical flagellum enables a bacterium to swim toward positive stimuli and away from danger. But how is the flagellum, composed of many different proteins, assembled? In a Perspective, Macnab explains how subunits of the protein flagellin flow down a channel inside the flagellum and are then added to its tip through the action of a rotating pentameric cap complex (Yonekura et al.).     

Microbiology. Simple hosts may help reveal how bacteria infect cells

Important human pathogens invade and harm simple organisms. What's more, these infections require many of the same bacterial genes needed to make mammals sick. These observations suggest that even though simple organisms aren't perfect models for complex hosts such as mammals, the basic mechanisms by which bacteria establish infections in the various organisms may be similar. As a result, the work may help microbiologists identify the host proteins involved in infections, thereby providing potential new targets for antibacterial drugs.     

Action at a distance along a DNA

A number of ways are known by which an event at one location on a DNA molecule can affect an event at a distant location on the same molecule. Three classes of mechanisms are described for such distal actions: tracking or translocation of a protein along a DNA, the association of two proteins bound at separate sites to form a DNA loop in between, and distal interactions that are affected by the topology of the DNA. The basic characteristics of each type of mechanism are discussed in terms of the known physicochemical properties of DNA. The various modes of action at a distance are often interrelated. Examples include the formation of positively and negatively supercoiled DNA loops by tracking and the strong effects of DNA topology on looping.