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

Abstract

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 histories 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-I (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 histonebinding proteins such as dNAP-1 in the assembly of chromatin.