At Genomicron, blogger T. Ryan Gregory links to a paper out of UCSC that delves into one form of noncoding DNA, endogenous retroviruses. He notes that "roughly 8% of the human genome is represented by ERVs, which are descendants of former exogenous retroviruses that became incorporated into the germline genome." The PNAS paper, published by David Haussler’s lab, found that more than one-third of p53 binding sites are accounted for by ERV copies with a p53 site, seriously shaping p53's transcriptional network.