A Self-Help Guide for a Trim Genome

摘要

An old puzzle in genetics, called the C-value paradox, is that the size and complexity of genomes are sometimes at odds with the complexity of their hosts. A partial solution to the paradox is provided by increasing evidence (for example, from genome sequencing) that genomes are much more than mere collections of genes. For one thing, eukaryotic organisms typically carry a variable load of relics of "selfish DNA"―such as "trans-posons"―that propagate themselves but serve no obvious purpose. Not surprisingly, organisms have developed mechanisms to control, if not eliminate, selfish DNA. On page 1581 of this issue, Yao and colleagues (1) report new evidence that the ciliated protozoan Tetrahymena thermophi-la uses an RNA-based recognition system with parallels to RNA interference (RNAi) to guide deletion of unnecessary DNA.