The packaging of chromatin at higher level requires additional set of proteins that collectively are referred as Non - histone chromosomal (NHC) proteins. Non - histone chromosomal proteins are of three types :
(i) Scaffold or structural NHC
(ii) Functional NHC protein e.g., DNA polymerase, RNA polymerase
(iii) Regulatory NHC protein e.g., HMG (High mobility group proteins that controls gene expression)