The interaction between Ran and NTF2 is required for cell cycle progression

The small GTPase Ran is required for the trafficking of macromolecules into and out of the nucleus. Ran also has been implicated in cell cycle control , specifically in mitotic spindle assembly. In interphase cells, Ran is pre dominately nuclear and thought to be GTP bound, but it is also present in t he cytoplasm, probably in the GDP-bound state. Nuclear transport factor 2 ( NTF2) has been shown to import RanGDP into the nucleus. Here, we examine th e in vivo role of NTF2 in Ran import and the effect that disruption of Ran imported into the nucleus has on the cell cycle. A temperature-sensitive (t s) mutant of Saccharomyces cerevisiae NTF2 that does not bind to Ran is una ble to import Ran into the nucleus at the nonpermissive temperature. Moreov er, when Ran is inefficiently imported into the nucleus, cells arrest in G( 2) in a MAD2 checkpoint-dependent manner. These findings demonstrate that N TF2 is required to transport Ran into the nucleus in vivo. Furthermore, we present data that suggest that depletion of nuclear Ran triggers a spindle- assembly checkpoint-dependent cell cycle arrest.