Internucleosomal

Internucleosomal is an adjective used in molecular biology to describe phenomena that occur between adjacent nucleosomes, the basic units of chromatin where about 147 base pairs of DNA wrap around a histone octamer. The term often refers to the linker DNA segment that connects consecutive nucleosomes, as well as events that act on or involve this region.

In chromatin structure, internucleosomal spacing describes the length and organization of linker DNA between nucleosomes. This spacing varies by species and cell type and influences chromatin compaction, accessibility, and the dynamics of transcription, replication, and repair. Histone H1 and chromatin remodelers modulate internucleosomal spacing, contributing to different higher-order chromatin states.

In apoptosis, internucleosomal cleavage denotes nuclease-mediated cutting of DNA within the linker regions between nucleosomes. This produces fragments that are multiples of the nucleosome repeat length, yielding a characteristic DNA ladder on agarose gels. The caspase-activated DNase (CAD) is a key enzyme driving this pattern during programmed cell death.

In research and diagnostics, internucleosomal DNA fragmentation serves as a biochemical hallmark of apoptosis and can inform studies of chromatin structure and chromatin remodeling. The term emphasizes the relationship between nucleosomes rather than the core particle itself.