SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1 is a protein that in humans is encoded by the SMARCB1 gene.

SWI/SNF (SWItch/Sucrose Non-Fermentable), is a nucleosome remodeling complex found in both eukaryotes and prokaryotes. In simpler terms, it is a group of proteins that associate to remodel the way DNA is packaged. It is composed of several proteins – products of the SWI and SNF genes (SWI1, SWI2/SNF2, SWI3, SWI5, SWI6) as well as other polypeptides.

It possesses a DNA-stimulated ATPase activity and can destabilise histone-DNA interactions in reconstituted nucleosomes in an ATP-dependent manner, though the exact nature of this structural change is unknown.

The human analogs of SWI/SNF are BAF (SWI/SNF-A) and PBAF (SWI/SNF-B). BAF in turn stands for “BRG1- or HBRM-associated factors”, and PBAF is for “polybromo-associated BAF”.