Formation of human long intergenic non-coding RNA genes and pseudogenes: ancestral sequences are key players

Pathways leading to formation of non-coding RNA and protein genes are varied and complex. We report finding a highly conserved repeat sequence present in both human and chimpanzee genomes that appears to have originated from a common primate ancestor. This sequence is repeatedly copied in human chromosome 22 (chr22) low copy repeats (LCR22) or segmental duplications and forms twenty-one different genes, which include human long intergenic non-coding RNA (lincRNA) gene and pseudogene families, as well as the gamma-glutamyltransferase ( GGT ) protein gene family and the RNA pseudogenes that originate from GGT sequences. In sharp contrast, only predicted protein genes stem from the homologous repeat sequence present in chr22 of chimpanzee. The data point to an ancestral DNA sequence, highly conserved through evolution and duplicated in humans by chromosomal repeat sequences that serves as a functional genomic element in the development of new and diverse genes in humans and chimpanzee.