DUF1220

DUF1220 is a protein domain of unknown function that shows a striking human lineage-specific (HLS) increase in copy number and may be important to human brain evolution. The copy number of DUF1220 domains increases generally as a function of a species evolutionary proximity to humans. DUF1220 copy number is highest in human (over 270, with some person-to-person variations). and shows the largest HLS increase in copy number (an additional 160 copies) of any protein coding region in the human genome. DUF1220 copy number is reduced in African great apes (estimated 125 copies in chimpanzees), further reduced in orangutan (92) and Old World monkeys (35), single- or low-copy in non-primate mammals and absent in non-mammals. DUF1220 domains are approximately 65 amino acids in length and are encoded by a two-exon doublet. In the human genome DUF1220 sequences are located primarily on chromosome 1 in region 1q21.1-q21.2, with several copies also found at 1p36, 1p13.3, and 1p12. Sequences encoding DUF1220 domains show signs of positive selection, especially in primates, and are expressed in several human tissues including brain, where their expression is restricted to neurons.