Final answer:
Histone tails are involved in the packaging of DNA in chromosomes, being part of basic proteins called histones found in the nucleus. They play a vital role in DNA packaging by forming nucleosomes and can undergo epigenetic changes that regulate gene expression without altering the DNA sequence.
Step-by-step explanation:
Among the options provided, the correct answer to the question of what is true of histone tails is that they are involved in the packaging of DNA in chromosomes. Histones are basic proteins, rich in the amino acids arginine and lysine, and are found in the cell nucleus. They form the protein component of nucleoprotein complexes that assist in tightly packing the DNA into structures known as nucleosomes. This is part of the DNA packaging process which organizes the long strands of DNA into a condensed, organized structure within the chromosome.
These histone tails can be modified through epigenetic changes such as acetylation, which results in the loose packing of nucleosomes. This modification does not change the DNA sequence but affects how tightly the histone and DNA interact, which can control gene expression by making certain regions of DNA more or less accessible for transcription. Importantly, these epigenetic changes to the histones allow movement of histones and can influence whether a chromosomal region should be open or closed to the transcription machinery.