Evolutionary conservation of a molecular machinery for export and expression of mRNAs with retained introns

Northern blot analysis of the zebrafish NXF1 mRNAs. Total RNA was extracted from adult zebrafish and selected with oligo(dT)-cellulose and analyzed on Northern blots as described in Materials and Methods. Blots containing mRNAs (5 µg/lane) were hybridized with either a zebrafish NXF1 exon-specific probe (left lane) or an intron 10-specific probe (right lane). The positions of molecular weight markers running in a parallel lane are indicated. The arrows point to the major bands discussed in the text.