Chromatin remodelling machines (CRMs) catalyse the decondensation of heterochromatin, to allow transcription to be stimulated. CRMs are recruited by the SAGA complex, which binds to upstream activator sequences. This allows the looping out of the gene needed from the tightly condensed structure of the heterochromatin. This process is typically completed by enzymes with a helicase activity, such as SWI/SNF. SWI/SNF uses ATP hydrolysis to provide the energy required to move nucleosomes along the DNA.