Figure 6.

The quality of transgenic sense transcripts determines the outcome of somatic transformation. Transgenes without (top) or with (bottom) 3′ non-coding sequences (yellow circles) are shown. Thin line, plasmid; thick arrow, Paramecium gene coding sequences; vertical green lines, telomeric repeats. In both cases, the transgenes are transcribed to produce sense (red) and antisense (blue) RNA. In the absence of 3′ non-coding sequences (top), the sense RNA transcripts either hybridize with the antisense transcripts to form dsRNA or serve as template for an RdRP, in either case leading to dsRNA formation which triggers gene silencing. In the presence of 3′ non-coding sequences (bottom), the 3′ processing signals make RNA processing efficient and/or sequester the sense transcripts before they can enter the gene silencing pathway or lead to dsRNA formation.