Acts as component of the nascent polypeptide-associated complex (NAC), which promotes mitochondrial protein import by enhancing productive ribosome interactions with the outer mitochondrial membrane. Also blocks the inappropriate interaction of ribosomes translating non-secretory nascent polypeptides with translocation sites in the membrane of the endoplasmic reticulum. BTT1 may act as a transcription factor that exert a negative effect on the expression of several genes that are transcribed by RNA polymerase II. Part of the nascent polypeptide-associated complex (NAC), consisting of EGD2 and either EGD1 or BTT1. NAC associates with ribosomes via EGD1 or BTT1. Predominantly cytoplasmic, may also transiently localize to the nucleus. Present with 1820 molecules/cell in log phase SD medium. Belongs to the NAC-beta family.