The initial step in Long Interspersed Element-1 (LINE-1) retrotransposition requires transcription from an internal promoter located within its 5′-untranslated region (5′-UTR). Previous studies have identified a YY1 (Yin Yang 1)-binding site as an important sequence in LINE-1 transcription. Here, we demonstrate that mutations in the YY1-binding site have only minor effects on transcription activation of the full-length 5′-UTR and LINE-1 mobility in a single round cultured cell retrotransposition assay. Instead, these mutations disrupt proper initiation of transcription from the +1 site of the 5′-UTR. Thus, we propose that the YY1-binding site functions as a component of the LINE-1 core promoter to direct accurate transcription initiation. Indeed, this sequence may explain the evolutionary success of LINE-1 by enabling full-length retrotransposed copies to undergo autonomous retrotransposition in subsequent generations.p. This work was\ud supported by a grant from the National Institutes of Health\ud (GM60518) awarded to J.V.M. J.N.A. was supported in part\ud by a University of Michigan Cancer Biology postdoctoral\ud training grant (CA009676) and then by a NRSA postdoctoral fellowship (F32GM20859). R.M.B. was supported by a\ud Wellcome Trust Project Grant (069702/Z/02/Z)
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