Gadd45a is an RNA binding protein and is localized in nuclear speckles.
BACKGROUND
The Gadd45 proteins play important roles in growth control, maintenance of genomic stability, DNA repair, and apoptosis. Recently, Gadd45 proteins have also been implicated in epigenetic gene regulation by promoting active DNA demethylation. Gadd45 proteins have sequence homology with the L7Ae/L30e/S12e RNA binding superfamily of ribosomal proteins, which raises the question if they may interact directly with nucleic acids.


RESULTS
Here we show that Gadd45a binds RNA but not single- or double stranded DNA or methylated DNA in vitro. Sucrose density gradient centrifugation experiments demonstrate that Gadd45a is present in high molecular weight particles, which are RNase sensitive. Gadd45a displays RNase-sensitive colocalization in nuclear speckles with the RNA helicase p68 and the RNA binding protein SC35. A K45A point mutation defective in RNA binding was still active in DNA demethylation. This suggests that RNA binding is not absolutely essential for demethylation of an artificial substrate. A point mutation at G39 impared RNA binding, nuclear speckle localization and DNA demethylation, emphasizing its relevance for Gadd45a function.


CONCLUSIONS
The results implicate RNA in Gadd45a function and suggest that Gadd45a is associated with a ribonucleoprotein particle.
Division of Molecular Embryology, DKFZ-ZMBH Alliance, Krebsforschungszentrum, Heidelberg, Germany.
Yuliya A
YA
Sytnikova
Andriy V
AV
Kubarenko
Andrea
A
Schäfer
Alexander N R
AN
Weber
Christof
C
Niehrs
D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D002460:Cell Line; D022003:Cell Nucleus Structures / Q000737:chemistry* / Q000648:ultrastructure; D053487:DEAD-box RNA Helicases / Q000378:metabolism; D019175:DNA Methylation; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D017354:Point Mutation; D011485:Protein Binding; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D012261:Ribonucleoproteins / Q000378:metabolism; D000068103:Serine-Arginine Splicing Factors; D014981:Xenopus; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D000097642:GADD45 Proteins
D018797:Cell Cycle Proteins; D053487:DEAD-box RNA Helicases; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; D000068103:Serine-Arginine Splicing Factors; D029867:Xenopus Proteins; C517171:Gadd45a protein, Xenopus; D000097642:GADD45 Proteins; C073288:SRSF2 protein, human
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