Figure 2.

Run-on transcription indicates that the silencing mechanism is post-transcriptional. (A) Immunofluorescence images of trichocysts in control and pT4– silenced cells. The control wild-type cell on the left has spindle-shaped trichocysts aligned at the plasma membrane. Only the trichocyst body is stained by an antibody that recognizes the whole family of TMPs; the tip by which the trichocyst is attached to the plasma membrane is not visible. The trichocysts in the silenced cell appear spherical and cannot attach to the plasma membrane or be secreted. Bar: 10 µm; 5 µm for the enlarged insets. (B) Run-on transcription of control and pT4– silenced cells. The probes fixed on the membrane are, from left to right, plasmid pGEM-T, the T1b, T2c and T4a coding regions, T4a 3′ sequences not present in the pT4– transgene construct and the β-tubulin PTBPT1 gene coding region as an invariant control. After hybridization of the membranes to nascent transcripts elongated in vitro in the presence of [α-³²P]UTP, the signals were quantified by phosphorimaging.