Playing chicken, single molecule

Many things happen to DNA. Proteins bind, slide along, dissociate. Sometimes they bump into each other, and then... what happens then?

This was exactly the question adressed in Finkelstein at al., Nature 2010. They were particularly interested in a bacterial protein called RecBCD, which is a powerful helicase. Using single-molecule microscopy they
had a look at what happens when RecBCD rams into some other protein.

And they had several to look at. RNA polymerase was the first one, and this is a formidable roadblock, and yet - RecBCD pushed it off the DNA with ease. Here are the actual images:

RecBCD sliding RNA polymerase along the DNA (76.5 %):

RecBCD ejecting RNA polymerase (8.5 %):

And RecBCD being stalled by RNA polymerase (rare events!) (15 %):

Then they tried other proteins, EcoRI endonuclease and lac repressor, and again, RecBCD was victorious over and over. Only the mighty nucleosome (never mind that it is a eukaryotic protein and it never met RecBCD before!) managed to put up a fight - 24% of the head-on collisions resulted with RecBCD being stalled, 11% resulted in nuceosome ejection and in remaining 65% RecBCD was sliding the nucleosome along the DNA.

What next? Well, now authors are preparing for experiments on RecBCD head-on collisions with Higgs bosons in the LHC.  I bet on RecBCD.

PS: it is all very convenient that the authors happened to study RecBCD - neat story, their protein is stronger than all the others, yay! But wat if they would have started with some lame one, like PNA polumerase? But hey! I never write my results in the order I get them... do you? Did THEY?

References:

Finkelstein IJ, Visnapuu ML, & Greene EC (2010). Single-molecule imaging reveals mechanisms of protein disruption by a DNA translocase. Nature, 468 (7326), 983-7 PMID: 21107319