ATP-facilitated chromatin assembly with a nucleoplasmin-like protein from Drosophila melanogaster

To gain a better understanding of the factors that can mediate chromatin assembly, we have purified and cloned a core histone-binding protein from Drosophila melanogaster embryos. This protein resembles Xenopus laevis nucleoplasmin, and it has therefore been termed dNLP, for Drosophila nucleoplasmin-like protein. dNLP is a nuclear protein that is present throughout development. Both purified native and recombinant dNLP bind to core histones and can function in the assembly of approximately regularly spaced nucleosomal arrays in a reaction that additionally requires DNA, purified core histones, ATP, and a partially purified fraction (containing at least one other assembly activity). We also analyzed the properties of an N-terminally truncated version of dNLP, termed dNLP-S, and found that the deletion of the N-terminal 31 residues of dNLP results in a loss of the specificity of the interaction of dNLP with core histones. We then compared the abilities of dNLP and Drosophila nucleosome assembly protein-1 (dNAP-1) to promote the decondensation of Xenopus sperm chromatin, a process that can be mediated by nucleoplasmin. We observed that dNAP-1, but not dNLP, was able to promote the decondensation of sperm chromatin. These and other data collectively suggest that dNLP may participate in parallel with other histone-binding proteins such as dNAP-1 in the assembly of chromatin.