KU ANTIGEN BINDS TO ALU FAMILY DNA

The GC-rich segment containing GGAGGC (Alu core) is conserved within t he RNA polymerase III (pol III) promoters of Alu family sequences. We have shown that the GGAGGC motif functions as a modulator of DNA repli cation as well as of transcription, and identified the proteins bindin g to the motif in human HeLa cells, In this study, the Alu core bindin g proteins were partially purified from human Raji cells by using an A lu core DNA affinity column, Both the proteins thus purified were impl ied to be subunits of Ku antigen based on the following criteria: The molecular weights of the proteins estimated on gel electrophoreses wer e 70 and 85 kDa, respectively, under denaturing conditions, while unde r non-denaturing conditions only one band was observed for the same sa mple at 150 kDa, probably representing hetero-dimer formed between the 70 and 85 kDa proteins, The sizes and the hetero-dimer formation are reminiscent of the 70 and 80 kDa subunits of Ku antigen (Ku-p70 and Ku -p80), Moreover, the purified proteins were immunoreactive with anti-K u antibodies, and the specific DNA-protein complex on the Alu core ele ment was cancelled by the anti-Ku antibodies, The nucleoprotein comple x showed the same clipping patterns as those of the complex between th e Alu core element and an authentically purified Ku antigen after prot eolytic cleavage with trypsin and chymotrypsin.