Region two held the surprise. It is called the proline-rich domain because it has high levels of the amino acid proline.
"There was no known function for a structure like the proline-rich domain, so we at first thought it did nothing more than connect the docking region of the protein with regions three and four," Suo says.
"Then by accident we learned that this was not just a structural connection, but that it is critical to the protein's ability to replicate DNA with very few mistakes."
For this study, Suo and his colleagues wanted to learn how efficiently the new protein made new DNA. But the researchers initially considered the protein too large and difficult to produce in the laboratory. So instead of making the entire protein, the researchers made only the part that does the repair work, regions three and four.
When they tested this short version of the protein, however, they found that it made up to a 100 times more mistakes than did the similar repair protein, DNA polymerase beta.
"That error rate is too high," Suo says. "If the entire repair protein produced that many errors, it would cause more problems than it would fix."
Next, the researchers made the entire protein and found that it could repair DNA as accurately as the comparison protein.
Last, they tested a version of the protein that lacked the docking region. This shortened molecule also accurately made DNA.
"To find that the proline-rich domain was responsible for this repair protein's high fidelity came as a complete surprise," Suo says.
Presently the scientists are studying the three-dimensional structure of the entire protein to learn how the presence of a proline-rich region influences the ability of the protein to accurately make DNA.
Source:Ohio State University