| Using the same yeast two hybrid screening system , we now show that Ku 70 also interacts with heterochromatin protein 1alpha ( HP1alpha ) , a protein known to be associated with telomeres as well as heterochromatin . ^^^ The interaction was also reproduced in vivo in HeLa cells , where endogenous Ku 70 coimmunoprecipitated with HP1alpha . ^^^ The interaction domains of Ku 70 and HP1alpha included the Leu Ser repeat ( amino acids 200 385 ) and the chromo shadow domain , respectively . ^^^ Ku 70 was largely colocalized with transfected HP1alpha but not with a C terminal deletion mutant , HP1alpha ( Delta ) C . ^^^ In contrast to HP1alpha , Ku 70 did not repress transcriptional activity of the reporter gene when tethered to DNA after transfection to mammalian cells . ^^^ |