Frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS) are neurodegenerative disorders with clinical, genetic, and neuropathological overlap. Aberrant cytoplasmic aggregation of FUS (fused in sarcoma) is associated with 3% of familial ALS and 10% of all FTLD cases (FTLD-FUS). FUS is a nuclear RNA/DNA binding protein with PY type nuclear localization signal present at its C-terminus which enables interaction with Transportin-1 and its transport into the nucleus. ALS patients with FUS positive cytoplasmic inclusions contain mutations in gene encoding FUS. The majority of these mutations fall within the nuclear localization signal which disables its transport to nucleus. On the other hand, patients with FTLD-FUS do not have FUS mutations but FUS still accumulates in cytoplasmic inclusions, suggesting a different mechanism of inclusion formation in ALS and FTLD. Our aim is to find out whether nuclear localization signal of FUS is subjected to posttranslational modifications that have impact on its localization. We have identified a novel posttranslational modification in nuclear localisation signal of FUS. This modification destroys interaction with Transportin-1 and consequentially affects transport of FUS into the nucleus. Our study implicates new posttranslational modifications as one of the mechanisms by which nuclear transport of FUS is regulated and potentially perturbed in ALS and FTLD.