SLACS in vitro transcription.
A. In vitro transcription reactions containing no added DNA (lane 1), the pXS2 backbone vector (lane 2) or pSLACS (lane 3) were performed in the presence of [α-32P]-GTP, and RNA products were analysed on an 8% polyacrylamide-7 M urea gel.
B. In vitro transcription reactions were carried out in the absence of radiolabelled nucleotides, and RNA was analysed by primer extension with an end-labelled oligonucleotide complementary to a 19 nt tag engineered in both the SLACS and SL templates (SLtag). U2 primer extension served as a loading control in both panels.