The cohesin complex mediates DNA-DNA interactions both between (sister chromatid 
cohesion) and within chromosomes (DNA looping). It has been suggested that 
intra-chromosome loops are generated by extrusion of DNAs through the lumen of 
cohesin's ring. Scc2 (Nipbl) stimulates cohesin's ABC-like ATPase and is 
essential for loading cohesin onto chromosomes. However, it is possible that the 
stimulation of cohesin's ATPase by Scc2 also has a post-loading function, for 
example driving loop extrusion. Using fluorescence recovery after photobleaching 
(FRAP) and single-molecule tracking in human cells, we show that Scc2 binds 
dynamically to chromatin, principally through an association with cohesin. 
Scc2's movement within chromatin is consistent with a 'stop-and-go' or 'hopping' 
motion. We suggest that a low diffusion coefficient, a low stoichiometry 
relative to cohesin, and a high affinity for chromosomal cohesin enables Scc2 to 
move rapidly from one chromosomal cohesin complex to another, performing a 
function distinct from loading.