SMARCAL1 is a member of the SWI/SNF family of proteins. Members of this family have helicase and ATPase activities and are thought to regulate transcription of certain genes by altering the chromatin structure around those genes. The encoded protein shows sequence similarity to the E. coli RNA polymerase-binding protein HepA. Mutations in this gene are a cause of Schimke immunoosseous dysplasia (SIOD), an autosomal recessive disorder with the diagnostic features of spondyloepiphyseal dysplasia, renal dysfunction, and T-cell immunodeficiency. HARP bound with higher affinity to forked DNA than to single-stranded DNA (sDNA) or double-stranded DNA (dsDNA). HARP had ATPase activity that was stimulated by forked DNA, and to a lesser extent by ssDNA and dsDNA.