Abstract
The nuclear localization signal (NLS) and nuclear export signal (NES) are key signatures of proteins for controlling nuclear import and export. The NIb protein of turnip mosaic virus (TuMV) is an RNA-dependent RNA polymerase (RdRP) that is absolutely required for viral genome replication. Previous studies have shown that NIb is a nucleocytoplasmic shuttling protein and contains four putative NES and four putative NLS motifs. Here, we analyzed the function of these NESs and NLSs, and identified two functional NESs and one functional NLS. Mutation of the identified functional NESs or NLS inhibited viral RNA accumulation and systemic infection. Exportin 1 (XPO1) is a nuclear export receptor that binds directly to cargo proteins harboring a leucine-rich NES and translocates them to the cytoplasm. We found that XPO1 contains two NIb-binding domains, which recognize the NLS and NES of NIb, respectively, to mediate the nucleocytoplasmic transport of NIb and promote viral infection. Taken together, these data suggest that the nucleocytoplasmic transport of NIb is modulated by XPO1 through its interactions with the functional NLS and NES of NIb to promote viral infection.
Highlights
Nuclear import and export that govern substrate exchange between the nucleus and the cytoplasm are crucial processes in any eukaryotic cell
1http://prodata.swmed.edu/LocNES/LocNES.php 2http://sourceforge.net/projects/nesmapper and conducted an agroinfiltration-mediated transient expression assay in the transgenic Nicotiana benthamiana plants that stably express red fluorescent proteins fused to histone 2B (RFP-H2B) to evaluate their nuclear export ability (Martin et al, 2009; Anderson et al, 2018)
Only NbXPO1a and its a1 fragment including the IBN_N domain (NbXPO1a-a1) were associated with nuclear inclusion protein b (NIb) NLSc in the nucleus. Together these results suggest that the two functional nuclear export signal (NES) and one functional nuclear localization signal (NLS) in NIb are responsible for nuclear export and import of NIb by binding to the CRM1_C domain and IBN_N domain of XPO1, respectively
Summary
Nuclear import and export that govern substrate exchange between the nucleus and the cytoplasm are crucial processes in any eukaryotic cell. The nucleocytoplasmic transport depends on a network of proteins that shuttle between the nucleus and cytoplasm, allowing substrate exchange through the nuclear pore complex (NPC). The NPC permits passive diffusion of ions and small molecules up to 9 nm in diameter or up to 70 kDa for globular proteins to gain access to the nucleus (Görlich and Kutay, 1999). This diffusion is reasonably fast only for proteins of up to 20–30 kDa, and molecules
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call