In cooperation with other chaperones, Hsp70s are key components that facilitate folding of de novo synthesized proteins, assist translocation of precursor proteins into organelles, and are responsible for degradation of damaged protein under stress conditions (Probable). Involved in polar nuclei fusion during female gametophyte development and is essential for the regulation of endosperm nuclei proliferation (PubMed:20080634). Involved in sperm nuclear fusion with central cell polar nuclei at fertilization, which is critical for normal endosperm nuclear proliferation (PubMed:31410484). Required for pollen development and pollen tube growth (PubMed:24486762). Possesses ATPase activity in vitro (PubMed:26186593). Binding to ERDJ3A activates the ATPase activity of BIP1. Interacts with ERDJ3B (PubMed:19763086). Interacts with PDIL1-4 (PubMed:21909944). Interacts with BZIP28 (via C-terminus) in the endoplasmic reticulum (ER) lumen (PubMed:23624714). Under ER stress, BIP1 dissociates from BZIP28, a transcription factor involved in ER stress responses (PubMed:23624714). Interacts with ERDJ3A (PubMed:26186593). Expressed in mature pollen grains, and pollen tubes. Down-regulated during seed maturation. Up-regulated during germination. Induced by heat shock (PubMed:11402207). Induced by DTT (PubMed:26186593). Bip1 and bip2 double mutation affects the fusion of polar nuclei during female gametophyte development (PubMed:20080634). Bip1 and bip2 double mutation affects pollen tube growth and length (PubMed:24486762). Bip1, bip2 and bip3 triple mutation is pollen lethal (PubMed:24486762). Bip1, bip2 and bip3 triple mutation affects female gametophyte development during the early stages (PubMed:26186593). Baeckstroem et al identified BIP1 in a Mediator complex pull-down assay and suggested that BIP1 could be a plant specific component of the Mediator complex (PubMed:17560376). However, no experimental evidence has been brought so far to confirm this hypothesis (Probable). Belongs to the heat shock protein 70 (TC 1.A.33) family. DnaK subfamily.