Abstract

Histones occur in equal amounts to DNA in the cell nucleus and are largely responsible for the compaction of the genome into chromatin via the formation of nucleosomes and higher‐order structures. Whereas two of the five histone types exhibit little structural variation, the remaining three occur in many variant tissue‐ or species‐specific forms. Multiple postsynthetic enzymatic modifications accompanying virtually any type of genome activity, together with the programmed appearance of many histone variants during sea urchin embryogenesis (and other differentiation events in a number of organisms) make histones a challenging enigma in eukaryotic molecular biology.