ABSTRACT
The nucleus contains proteins synthesized in the cytoplasm. The molecular mechanisms by which these proteins accumulate into the nucleus remain unknown. Nuclear targeting sequences are suspected to recognize specific receptors. In an attempt to identify genes coding for such receptors, use was made of cytochrome cl. This protein is located in the inner membrane of the yeast mitochondria. The MATα2 gene product appears to be a nuclear protein. Histones are proteins closely associated with DNA. The subcellular location of the hybrid proteins was determined by indirect immunofluorescence using anti-β-galactosidase antibodies. Cells bearing the GAL4-CYT1 fusion were mutagenized to induce mutants defective in nuclear protein localization. Transport of proteins from the cytoplasm into the nucleus appears to be dependent on specific interaction of a short amino acid sequence within the transported protein and a putative receptor at the nucleus. Yeast nuclear proteins were extracted, electrophoresed through SDS polyacrylamide gel, and transferred to nitrocellulose.
