Repeat A monomers additively contribute to silencing. (A) Human repeat A sequence consists of 8.5 copies of a well-conserved CG-rich core and T-rich spacer sequences. Palindromic sequences hypothesized to form a secondary structure are underlined. Artificial repeat A was constructed as a 9-mer repetition of consensus monomer sequence and restriction enzyme sites were introduced to allow for the creation of shorter constructs. (B) Enhanced Green Fluorescent Protein gene (EGFP) expression following five days of transgene induction as measured by qRT-PCR, relative to d0 and normalized to changes in expression caused by induction of the vector alone and to ACTB expression for two biological replicates. (C) EGFP expression was measured by flow cytometry every 2 days for 16 days following induction of repeat A 2-mer. Data are normalized to EGFP expression in cells that were not induced with DOX.