( Understanding medical research problems...)Protein splicing upsets the DNA colinearity paradigm

Understanding medical research problems often relies on the direct, linear relationship between the sequence of a protein and the DNA encoding that protein. In fact, colinearity of DNA and protein sequences is thought to be a fundamental feature of the universal genetic code. However, a paper published today in Science by a team from the Brussels Branch of the global Ludwig Institute for Cancer Research (LICR) and the Seattle-based Fred Hutchinson Cancer Research Center (FHCRC), shows that a protein can be rearranged so that it is no longer colinear with its encoding DNA.

Genes have stretches of (protein) coding DNA sequences interspersed with stretches of non-coding DNA sequences. The first step in making the protein is the faithful transcription of the entire gene's sequence into an RNA sequence. The RNA is then 'spliced' such that the non-coding sequences are removed and the coding sequences are assembled in a linear fashion to form the template for translation from RNA to protein.

"Until now it was thought that colinearity of DNA and protein sequences was only interrupted by RNA splicing," says LICR's Dr. Benoit Van den Eynde, the study's senior author. "This new study shows that protein splicing also occurs, and may even result in protein fragments, or peptides, being spliced together in the order opposite to that which occurs in the parental protein."

According to Dr. Van den Eynde, this novel phenomenon occurs during the physiological function of 'antigen processing,' which produces antigenic peptides; the 'red flags' that mark cells for destruction by the immune system.

The immune system attacks 'foreign' cells - be they tumor cells, virally infected, or donated by another person - when T lymphocytes recognize antigenic peptides displayed on the cell surface. The antigens are created by 'proteasomes,' components of the cell machinery that cut foreign proteins into peptides that are then displayed on the cell surface fo
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Source:Ludwig Institute for Cancer Research

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