Increased Transcriptional Repression Correlates with Repeat Length. (a) Primer extension analysis of transcripts from the HSV-TK promoter adjacent to increased lengths of (CGG)n triplet repeat. None: no injected DNA, CAT: 0.3 ng pCMV-CAT alone. All other lanes represent co-injections of 3 ng of reporter DNA and 0.3 ng of control (pCMV-CAT) DNA per ooctye. Lane 1: pHSVtk-CAT vector; Lane 2: methylated pHSVtk-CAT vector. Lanes 3 to 6: pHSVtk-CAT containing 27, 70, 105 and 140 (CGG) triplet repeats, respectively (un-methylated). Post injection, oocytes were incubated for 18 hours at 18°C. Each extension reaction used RNA from 7 oocytes. (b) A graphical representation of the relative transcription from the HSV-TK promoter after normalisation to the co-injected pCMV-CAT control and for background signal. Lane numbers correspond to those in panel A.