THE YEAST NASCENT POLYPEPTIDE-ASSOCIATED COMPLEX INITIATES PROTEIN TARGETING TO MITOCHONDRIA IN-VIVO

The yeast nascent polypeptide-associated complex (NAC) is encoded by t wo genes, EGD1 and EGD2, and is associated with cytoplasmic ribosomes. Yeast mutants lacking NAC (Delta egd2) are viable but suffer slight d efects in the targeting of nascent polypeptides to several locations i ncluding the endoplasmic reticulum and mitochondria. If both NAC and M ft52p are missing from yeast cells, inefficient targeting of mitochond rial precursor proteins leads to defects in both mitochondrial functio n and morphology, We suggest that NAC provides a ribosomal environment for nascent mitochondrial targeting sequences to achieve secondary st ructure, thereby enhancing the efficiency of protein targeting.