Relevance of nuclear localization and functions of RNA helicase A.

RNA helicase A (RHA) regulates gene expression at transcriptional and post-transcriptional levels. It is also known that RHA shuttles between the nucleus and the cytoplasm. RHA possesses nuclear transport domain which functions as a nuclear localization signal (NLS) and nuclear export signal (NES), and predominantly localizes in the nucleus. Here, we identified regions that influence cellular localization of RHA. We showed that double-stranded RNA binding domain I and II (dsRBD I and II) positively localized to the cytoplasm. Mutational analysis revealed that RNA-binding ability was important to localization of dsRBD to the cytoplasm. RHA mutants lacking association with Pol II complexes were partially spilled from the nucleus. Furthermore, a minimal transactivation domain (MTAD), which is minimal region to interact with Pol II complexes, mainly localized to the nucleus in comparison with GFP. Our results indicated that the intracellular localization of RHA might be regulated by not only NLS and NES but also functional domains.