"Sloppier Copier" Mysteries Solved

Myron Goodman, Ph.D.,
University of Southern California
NIEHS Grant R01ES012259

New discoveries by University of Southern California biologists solved a vexing question about the role of the protein RecA in DNA repair. These researchers also discovered the exact composition of the active form of the DNA repair enzyme polymerase V.

RecA is a nucleoprotein filament which is a long line of proteins bound to a single-stranded DNA. Experiments demonstrated that RecA transfers two molecules to polymerase V resulting in the enzymes activation. The molecules transferred are ATP for fuel, and a single RecA protein, one of many that make up the filament. RecA does not actively participate in the repair process; its role is merely to activate polymerase V. As soon as the molecules attach, polymerase V begins walking down the damaged DNA segment copying a new strand. As soon as it reaches the end of the damaged section, it drops off the DNA and immediately deactivates. It must be reactivated by RecA to copy more DNA, which is different than all other DNA polymerases.

Polymerase V was discovered in this laboratory in 1999 as was nicknamed the “sloppier copier” because it makes frequent copying mistakes which show up as mutations in the cell’s DNA. The researchers postulate that polymerase V may be more important for the long-term success of a species than its more accurate counterparts. Some of the mutations are likely to be helpful, enabling organisms to better adapt to their environments. These helpful mutations then spread through the species by natural selection.

Citation: Jiang Q, Karata K, Woodgate R, Cox MM, Goodman MF. The active form of DNA polymerase V is UmuD’2C-RecA-ATP. Nature. 2009 July 16; 460(7253): 359-63.