Ran binds to chromatin by two distinct mechanisms

Ran GTPase plays important roles in nucleocytoplasmic transport in interphase [1, 2] and in both spindle formation and nuclear envelope (NE) assembly during mitosis [3, 4, 5]. The latter functions rely on the presence of high local concentrations of GTP-bound Ran near mitotic chromatin [3, 4, 5]. RanGTP localization has been proposed to result from the association of Ran's GDP/GTP exchange factor, RCC1, with chromatin [6, 7, 8, 9], but Ran is shown here to bind directly to chromatin in two modes, either dependent or independent of RCC1, and, where bound, to increase the affinity of chromatin for NE membranes. We propose that the Ran binding capacity of chromatin contributes to localized spindle and NE assembly.