Fig. 3.

Mbf1 protein directly counteracts 5′-3′ exoribonuclease activity in vivo and in vitro. (A) mbf1²/hs-pcm double heterozygotes exhibit the Polycomb phenotype in the wild-type Polycomb group background. *P<0.01. (B) Recombinant Drosophila Mbf1 and Pcm preparations were resolved by 5-20% SDS-PAGE and the gel stained with Coomassie Brilliant Blue. (C) Recombinant Drosophila Mbf1 inhibits Pcm activity in vitro. In vitro-transcribed E(z) RNA [IVTed E(z) RNA] was used as substrate for Pcm. Reactions included the indicated components, and purified RNAs were resolved on a 1.5% agarose gel. dsDNA marker size is indicated (bp). Amounts of Mbf1 added: +, 2.5 µg; ++, 5 µg; ++++, 10 µg.