Minor spliceosome, major surprise: it's cytoplasmic

One of the great surprises of modern biology was the discovery of introns and the consequent understanding that gene transcripts are spliced to form mature messenger RNA (mRNA). A further surprise was the recent discovery that there are two kinds of splicing systems, the major and minor, which act on different types of introns. Now, Harald König, Ferenc Müller (Institute for Toxicology and Genetics, Karlsruhe, Germany), and colleagues uncover yet one more surprise: the minor system acts not in the nucleus, but in the cytoplasm.

The minor spliceosome, found primarily in plants and animals, edits less than 1% of all introns, which are characterized by unique sequences at the splice sites. All genes containing minor introns also contain major introns, which are...