DDP1, a single-stranded nucleic acid-binding protein of Drosophila, associates with pericentric heterochromatin and is functionally homologous to theyeast Scp160p, which is involved in the control of cell ploidy

The centromeric dodeca-satellite of Drosophila forms altered DNA structures in vitro in which its purine-rich strand (G-strand) forms stable fold-back structures, while the complementary C-strand remains unstructured. In this paper, the purification and characterization of DDP1, a single-stranded DN A-binding protein of high molecular mass (160 kDa) that specifically binds the unstructured dodeca-satellite C-strand, is presented. In polytene chrom osomes, DDP1 is found located at the chromocentre associated with the peric entric heterochromatin but its distribution is not constrained to the dodec a-satellite sequences. DDP1 also localizes to heterochromatin in interphase nuclei of larval neuroblasts. During embryo development, DDP1 becomes nucl ear after cellularization, when heterochromatin is fully organized, being a lso associated with the condensed mitotic chromosomes. In addition to its l ocalization at the chromocentre, in polytene chromosomes, DDP1 is also dete cted at several sites in the euchromatic arms co-localizing with the hetero chromatin protein HP1. DDP1 is a multi-KH domain protein homologous to the yeast Scp160 protein that is involved in the control of cell ploidy. Expres sion of DDP1 complements a Delta scp160 deletion in yeast. These results ar e discussed in view of the possible contribution of DNA structure to the st ructural organization of pericentric heterochromatin.