Final answer:
Histone protein H4 is part of the histone octamer core of a nucleosome, around which DNA is tightly wrapped in eukaryotic cells. These histone-DNA complexes are essential for compacting DNA into chromatin and are found in both transcriptionally active and inactive regions.
Step-by-step explanation:
In eukaryotic DNA, histone protein H4 is most likely to be found in the core of a nucleosome. Eukaryotic DNA is organized into a compact structure where DNA wraps around a group of histone proteins to form nucleosomes.
Each nucleosome consists of DNA wound around an octamer of histones that includes two copies each of H2A, H2B, H3, and H4. These core histones are strongly basic due to their lysine and arginine residues, allowing them to bind tightly to the negatively charged DNA.
During the interphase, histones are found throughout chromatin, both in regions of euchromatin, where genes are actively transcribed, and in heterochromatin, where DNA is more tightly packed and generally transcriptionally inactive.
However, H4, along with the other core histone proteins, is a principal component of nucleosomes and is essential for DNA packing throughout the cell cycle.