Activated PLK1 phosphorylates GTSE1 on serine residue S435, located in immediate vicinity of the GTSE1 nuclear localization signal (NLS) R431RR433 (Arg431Arg432Arg433). PLK1-mediated phosphorylation promotes GTSE1 nuclear translocation, possibly by exposing the NLS of GTSE1 to the nuclear import machinery. PLK1 can also phosphorylate human GTSE1 on serine residue S233. S233 is not evolutionarily conserved and is therefore not shown (Liu et al. 2010).