What is the basic unit of DNA packaging in eukaryotes called?

The nucleosome is the basic unit of DNA packaging in eukaryotes.

A nucleosome consists of a stretch of DNA wrapped around a protein core called a histone octamer. The structure resembles thread wound around a spool. About 146 base pairs of DNA make roughly 1.67 turns around the core, helping compress the enormous length of genetic material so it can fit inside a cell nucleus.

Nucleosomes form the fundamental repeating units of chromatin. Neighboring nucleosomes are connected by linker DNA, producing the classic “beads-on-a-string” appearance. Chromatin is then folded and organized into higher levels of structure, eventually contributing to chromosomes. Histone proteins are therefore components of nucleosomes, not the name of the complete packaging unit.

Nucleosomes also regulate access to DNA. Chemical modifications on histone tails and changes in nucleosome position can make particular DNA regions more or less accessible to proteins involved in transcription, replication, and repair. The particles were first observed by electron microscopy in 1974.