Figure 9.

Model for the Protective Role of the A Element in RNA Silencing.

In GUS-silenced (−A) plants, read-out transcription from the GUS transgene continues to include the nos polyadenylation region, vector sequences, and plant flanking DNA. These chimeric transcripts could be converted to dsRNA via RNA-dependent RNA polymerase using flanking DNA–derived siRNA for attenuation and drag all sequences contained in the transcript into the silencing machinery. The protective role of the A element is in preventing read-out transcription from reaching the flanking DNA.