University of Dublin researchers David Knowles and Aoife McLysaght, of the Smurfit Institute of Genetics, have identified three uniquely human genes that are not found in any other species. The researchers went on to investigate similar sequences in chimpanzees and other primates but discovered that in these animals the sequences do not code for proteins - suggesting that the three human-specific genes found in their studies may have originated from 'junk' or non-coding primate DNA.

Many past studies have identified genes that have been rearranged or duplicated through evolution, taking on different functions in different organisms. Much less is known about whether new genes have ever originated from non-coding sequence, and how exactly the translation occurs.

Through extensive sequence analysis, using the BLASTP protein tool, the researchers identified three proteins in humans that did not have any BLASTP hits in chimps. The three genes were identified as: CLLU1, which codes for the chronic lymphocytic leukemia upregulated gene 1, as well as C22orf45 and DNAH10OS, which are less well characterized.

A dozen nucleotide substitutions spanned these three genes. Seven of these substitutions (four synonymous and three non-synonymous) appear to have occurred in the chimp genome, where sequences for the genes are present but non-coding. Meanwhile, five substitutions — three non-synonymous — occurred in the human genome.

Based on these findings and their subsequent analyses, the team concluded the genes originated in parts of the genome that are non-coding in other primates.

Although the functions of the genes are poorly understood, the researchers noted that all three overlap with genes on the opposite DNA strand. In addition, each produces an intronless ORF (open reading frame) coding for a short protein.

"They are unlike any other human genes and have the potential to have a profound impact," McLysaght, a molecular evolution researcher at the University of Dublin, said in a statement.

Based on these findings, the team estimates that about 0.075 percent of human genes — roughly 18 of the 24,000 — are human-specific and arose from formerly non-coding sequence.

"The three genes reported here are the first well-supported cases of protein-coding genes that arose in the human lineage and are not found in any other organism," Knowles and McLysaght concluded. "It is tempting to infer that human-specific genes are at least partly responsible for human-specific traits and it will be very interesting to investigate the functions of these novel genes."

Published in the online edition of Genome Research. Abstract: http://genome.cshlp.org/content/early/2009/08/31/gr.095026.109.abstract

Source: http://www.genomeweb.com//node/923186?emc=el&m=481924&l=1&v=a34d2debfe