Co-chaperone that binds misfolded and hydrophobic patches-containing client proteins in the cytosol. Mediates their targeting to the endoplasmic reticulum but also regulates their sorting to the proteasome when targeting fails (PubMed:28104892). Functions in tail-anchored/type II transmembrane proteins membrane insertion constituting with ASNA1 and the BAG6 complex a targeting module (PubMed:28104892). Functions upstream of the BAG6 complex and ASNA1, binding more rapidly the transmembrane domain of newly synthesized proteins (PubMed:28104892, PubMed:25535373). It is also involved in the regulation of the endoplasmic reticulum-associated misfolded protein catabolic process via its interaction with BAG6: collaborates with the BAG6 complex to maintain hydrophobic substrates in non-ubiquitinated states (PubMed:23129660, PubMed:25179605). Competes with RNF126 for interaction with BAG6, preventing the ubiquitination of client proteins associated with the BAG6 complex (PubMed:27193484). Binds directly to HSC70 and HSP70 and regulates their ATPase activity (PubMed:18759457). (Microbial infection) In case of infection by polyomavirus, involved in the virus endoplasmic reticulum membrane penetration and infection via interaction with DNAJB12, DNAJB14 and HSPA8/Hsc70 (PubMed:24675744). Homodimer (PubMed:15708368). Homooligomer (By similarity). Interacts with DNAJC5 and DNAJC5B. Interacts (via TPR repeats) with HSP90AA1 (PubMed:15708368). Interacts (via Gln-rich region) with SLC2A1 (PubMed:15708368). Interacts with HSP90AB1 (PubMed:16580629). Interacts (via TPR repeats) with HSPA8/Hsc70; the interaction is direct (PubMed:24675744). Interacts with BAG6 (via ubiquitin-like domain); interaction prevents interaction between BAG6 and RNF126 (PubMed:23129660, PubMed:25179605, PubMed:27193484). Forms a multiprotein complex, at least composed of DNAJB12, DNAJB14, HSPA8/Hsc70 and SGTA; interaction with DNAJB14 and HSPA8/Hsc70 is direct (PubMed:24675744). (Microbial infection) Interacts with Vpu and Gag from HIV-1. (Microbial infection) Interacts with SARS-CoV accessory protein 7a. Co-localizes with HSP90AB1 in the cytoplasm. Increased nuclear accumulation seen during cell apoptosis. Ubiquitous. The second tetratricopeptide repeat (TPR 2) mediates the interaction with SARS-CoV accessory protein 7a. Belongs to the SGT family.