Strategies to distinguish between the function of a lncRNA product and its transcription. Both DNA strands are shown as separate boxes to indicate a lncRNA transcribed from the top reverse strand, overlapping a pc gene transcribed from the bottom forward strand in antisense orientation. A silencing function of the lncRNA can be predicted by an anti-correlating expression pattern. (a) Left: the lncRNA silencing effect is mediated by tethering of the lncRNA product at the site of transcription, sequence-specific binding of an EM to the lncRNA and guidance of the EM to the pc gene promoter. Right: silencing is mediated by a transcription process independent of the lncRNA product. (b) Posttranscriptional knockdown removes the lncRNA product, thus reversing a lncRNA product-mediated effect (left) but not the transcription-mediated effect (right). (c) lncRNA promoter deletion removes both lncRNA product- (left) and transcription-mediated (right) effects. (d) Truncation experiments inserting transcriptional stop signals at different positions within the lncRNA gene identify the functional region of the lncRNA gene (RNAPII is not shown). Left: lncRNA is only functional when the region corresponding to EM binding site is present. Right: lncRNA is only functional when it crosses the promoter of the overlapped pc gene. For details see Figure 1g, Figure 2e, Figure 3c, Figure 4d and text.