IDENTIFICATION AND MOLECULAR-CLONING OF YEAST HOMOLOG OF NUCLEOSOME ASSEMBLY PROTEIN-I WHICH FACILITATES NUCLEOSOME ASSEMBLY INVITRO

Yeast DNA coding for nucleosome assembly protein I (NAP-I), which facilitates nucleosome assembly in vitro at physiological ionic conditions, was cloned and its gene product was characterized. A monoclonal antibody against NAP-I (58 kDa) from human HeLa cells was used to screen a genomic library of Saccharomyces cerevisiae constructed into lambda-gt11. A 60-kDa protein was detected by immunoblotting in the extracts of Escherichia coli lysogenized with a positive clone. The 60-kDa protein purified from the extracts had an activity equivalent to that of NAP-I from mouse and human cells. The amino acid sequence deduced from the gene coding for the yeast NAP-I defines a polypeptide of molecular mass 47,848 Da with three negatively charged regions. While the two regions contain 8 and 10 acidic amino acids out of 13 amino acid residues, the longest stretch has 15 glutamic and 13 aspartic acids out of 38 residues. These regions are probably involved in the interaction with histones. Proteins recognized by the anti-NAP-I antibody were also present in Xenopus oocytes and Drosophila cultured cells. Possible roles of NAP-I are discussed in relation to other nucleosome assembly proteins.