Mediates feedback control of cholesterol synthesis by controlling SCAP and HMGCR. Functions by blocking the processing of sterol regulatory element-binding proteins (SREBPs). Capable of retaining the SCAP-SREBF2 complex in the ER thus preventing it from escorting SREBPs to the Golgi. Seems to regulate the ubiquitin-mediated proteasomal degradation of HMGCR. May play a role in growth and differentiation of tissues involved in metabolic control. May play a regulatory role during G0/G1 transition of cell growth.

Expressed in all tissues tested with highest expression in the liver.

Belongs to the INSIG family.

Ubiquitinated. Subsequent to sterol deprivation, the SCAP-SREBF2 complex becomes dissociated from INSIG1, is then ubiquitinated and degraded in proteasomes. Although ubiquitination is required for rapid INSIG1 degradation, it is not required for release of the SCAP-SREBP complex. Ubiquitinated by RNF139.

Endoplasmic reticulum membrane.