Faktoren des Kerntransports von Core-Histonproteinen: Strukturelle und funktionelle Analyse

Abstract

Core histones are small basic proteins which form the nucleosomes in eukaryotic chromatin. In vitro nuclear import studies show that the four core histones H2A, H2B, H3 and H4 do not enter the nucleus by diffusion, but by an active and receptor-mediated process which requires nuclear localisation signals (NLS). Transfection studies show that core histones contain at least two portions which can function as NLS. Two structurally different types are distinguished: One is formed by a single stretch of basic amino acids and is located within the amino terminal domain, the second contains the entire hydrophobic globular domain. In vitro competition studies showed that the core histones are imported into the nucleus by a different pathway from the H1-linker histones and the proteins containing a classical NLS. Reconstitution experiments identified importin-beta, importin7, importin5 and transportin as functional import receptors for the nuclear import of the four core histones.