Guardian at the gate: preventing unspliced pre-mRNA export.

The production of a mature mRNA requires the assembly and cooperation of numerous complexes before nuclear export. The deleterious effects of intron-containing pre-mRNA leakage into the cytoplasm necessitate mechanisms to prevent premature export of partially processed or unprocessed messages. A new study demonstrates that the Saccharomyces cerevisiae protein Mlp1 specifically retains intron-containing pre-mRNAs in the nucleus.