[4] Despite often being noncoding DNA,[6] some ultraconserved elements have been found to be transcriptionally active, producing non-coding RNA molecules.
[7] Researchers originally assumed that perfect conservation of these long stretches of DNA implied evolutionary importance, as these regions appear to have experienced strong negative (purifying) selection for 300-400 million years.
[4] Ultraconserved elements are not exempt from mutations, as exemplified by the presence of 29,983 polymorphisms in the UCE regions of the human genome assembly GRCh38.
[11] Computational analysis of human ultraconserved noncoding elements (UCNEs) found that the regions are enriched for A-T sequences and are generally GC poor.
[3][4][13] A study comparing ultraconserved elements between humans and the Japanese puffer fish Takifugu rubripes proposed an importance in vertebrate development.
[14] Double-knockouts of UCEs near the ARX gene in mice caused a shrunken hippocampus in the brain, though the effect was not lethal.
[5][9] For example, UCRs tend to accumulate less mutations than flanking segments, in both neoplastic and non-neoplastic samples from persons with hereditary non-polyposis colorectal cancer.