Structural maintenance of chromosomes (SMC) complexes shape the genomes of 
virtually all organisms, but how they function remains incompletely understood. 
Recent studies in bacteria and eukaryotes have led to a unifying model in which 
these ring-shaped ATPases act along contiguous DNA segments, processively 
enlarging DNA loops. In support of this model, single-molecule imaging 
experiments indicate that Saccharomyces cerevisiae condensin complexes can 
extrude DNA loops in an ATP-hydrolysis-dependent manner in vitro. Here, using 
time-resolved high-throughput chromosome conformation capture (Hi-C), we 
investigate the interplay between ATPase activity of the Bacillus subtilis SMC 
complex and loop formation in vivo. We show that point mutants in the SMC 
nucleotide-binding domain that impair but do not eliminate ATPase activity not 
only exhibit delays in de novo loop formation but also have reduced rates of 
processive loop enlargement. These data provide in vivo evidence that SMC 
complexes function as loop extruders.