Important messages require accurate transmission. Big genes are especially challenging because they combine many coding segments (exons) that lie between long stretches of non-coding elements (introns). During processing, introns are snipped out and exons pasted together to form a template for proteins called messenger RNA (mRNA). Mistakes in RNA processing can reduce the expression of a functional protein or, worse, produce an abnormal protein that interferes with normal cell behavior. But just how a cell's molecular machinery eliminates long introns without making errors has puzzled scientists for years.