UniProt SUBCELLULAR LOCATION for Dsup (P0DOW4) records nuclear localization with experimental backing from PMID:27649274 (Dsup-GFP co-localization with nuclear DNA in S2/HEK293T cells and IHC in tardigrade embryos). This mapping reference converts the controlled-vocabulary nuclear location into the GO:0005634 (nucleus) annotation with IEA evidence.

Dsup identified as a tardigrade-unique nuclear protein that associates with DNA

Expression of Dsup in human HEK293T cells suppresses X-ray-induced DNA damage (SSBs and DSBs)

Dsup improves radiotolerance when expressed in human cells

Dsup shields DNA from reactive oxygen species (ROS) including hydrogen peroxide

C-terminal region (aa 208-445) is required and sufficient for DNA binding and nuclear co-localization

Dsup binds preferentially to nucleosomes over free DNA

Dsup binds primarily to the nucleosome core rather than linker DNA

Can be incorporated into periodic nucleosome arrays without disrupting chromatin structure

Co-binds with histone H1 simultaneously on nucleosomes

C-terminal region (aa 360-445) required for nucleosome binding and hydroxyl radical protection

Conserved region has sequence similarity to HMGN nucleosome-binding domain

Mutagenesis of RRSSR (363-367) to EESSE decreases nucleosome binding

H. exemplaris ortholog has conserved nucleosome binding and DNA protection function

Protects chromatin from hydroxyl radical-mediated cleavage in purified biochemical system

Dsup experimentally confirmed as intrinsically disordered protein by SAXS and CD spectroscopy

Forms fuzzy complex with DNA rather than rigid binding

Has RNA-binding ability in addition to DNA binding

Dsup binds RNA directly in vitro - incubation of Dsup with total D. melanogaster RNA produced a dose-dependent gel mobility shift, the primary experimental demonstration of Dsup RNA-binding activity.

Dsup expression enhances radioresistance and lifespan in D. melanogaster under gamma irradiation.

Dsup acts as a non-specific repressor of transcription; >99% of differentially expressed genes in Dsup-expressing flies were down-regulated.

Dsup binds DNA non-sequence-specifically, with higher affinity for nucleosomes than free DNA, can simultaneously bind histone H1 and interacts with histone tails; recent work also reports RNA binding, consistent with the highly charged, intrinsically disordered nature of the protein.

In HEK293 cells expressing Dsup, DNA fragmentation after X-ray irradiation is significantly reduced in comet assays at 5-10 Gy and gamma-H2AX foci are reduced at 1 Gy; at 4 Gy Dsup-expressing cells retain proliferation whereas controls decline, and the benefit is abolished by knockdown of Dsup.

Heterologous Dsup expression confers radiotolerance and oxidative stress tolerance in non-tardigrade systems (human cultured cells, yeast, plants, fly), supporting a transferable, cell-autonomous DNA-protection mechanism rather than one requiring tardigrade-specific partners.