Mutation of the core repeat A sequences abrogates its silencing ability. (A) Sequence of the canonical repeat A monomer and four mutant constructs that were created to target the hypothesized repeat A hairpins. Underlined sequences correspond to stem 1 and stem 2. Dashes indicate no sequence change. (B) Mean Enhanced Green Fluorescent Protein gene (EGFP) expression following five days of transgene induction, measured by flow cytometry, relative to d0 (two-tailed paired t-test). Error bars indicate ± 1 S.D. of two single-cell clones. (C) EGFP and hygromycin (Hyg) gene expression following five days of transgene induction, measured by qRT-PCR, relative to d0 and normalized to ACTB expression for two independent single-cell clones.