Figure 7.

PTB repression of FAS exon 6 requires di-domain RNA contacts by RRMs 3 and 4. (A) Linear representation of PTB with RRMs and the RRM3-4 linker colour coded as in previous figures. RRMs are depicted with the longest side representing the RNA-binding β-sheet face. In panels B–G RRM1 and 3 are depicted binding at the URE6. (B) PTB is inhibitory when RRM3 binds at URE6 and RRM4 binds at a downstream YC dinucleotide, even when the proximal UC is mutated (C). PTB is not inhibitory when either RRM4 (D) or RRM3 (E) have an RNA binding mutation or when RRM3-4 packing is disrupted (F). Inhibitory activity is reduced when the surface positive charge organized by di-domain packing is reduced (G).