Effect of Ku proteins on IRES-mediated translation.
BACKGROUND
Ku is an abundant nuclear heterodimeric protein composed of 70 and 86 kDa subunits. As an activator of the catalytic subunit of DNA-PK (DNA-dependent protein kinase), Ku plays an important role in DNA repair and recombination. Ku is also involved in actions independent of DNA-PK, such as transcription regulation and telomere maintenance. Although Ku is localized in the cytoplasm under specific cellular conditions, no functions for Ku outside of the nucleus have as yet been reported. In addition to DNA binding, Ku binds specific RNA sequences with high affinity. However, no specific cellular mRNA targets for Ku have been identified.


RESULTS
In a yeast three-hybrid system, Ku70 bound to an RNA bait that contained an IRES (internal ribosomal entry site) element. A single band with migration properties similar to those of Ku70 was immunoprecipitated with anti-Ku antibody, using UV cross-linked complexes formed by HeLa cell nuclear extracts and an IRES-containing RNA probe. IRES activity was reduced in Ku80(-/-) cells. Overexpression of Ku proteins stimulated IRES-dependent translation.


CONCLUSIONS
The present study suggests that Ku binds IRES elements within RNA molecules, and that Ku plays a role in the modulation of IRES-mediated mRNA translation.
Silvera
Deborah
D
Department of Cell Research and Immunology, George S. Wise Faculty of Life Science, Tel Aviv University, Tel Aviv 69978, Israel.
Koloteva-Levine
Nadejda
N
Burma
Sandeep
S
Elroy-Stein
Orna
O
D000818:Animals; D034961:Antigens, Nuclear / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000378:metabolism*; D015870:Gene Expression; D006367:HeLa Cells; D006801:Humans; D000072200:Ku Autoantigen; D051379:Mice; D011485:Protein Binding; D014176:Protein Biosynthesis / Q000235:genetics*; D012313:RNA / Q000378:metabolism; D020798:Two-Hybrid System Techniques
D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D012313:RNA; C000606509:Xrcc6 protein, human; C000606510:Xrcc6 protein, mouse; D000072200:Ku Autoantigen