DNA Polymerase

Watson and Crick’s classic paper describing the chemical structure of DNA appeared in 1953, causing initial skepticism by some scientists about its significance. Watson-Crick suggested in their paper that a mechanism for copying DNA remained to be determined. American biochemist Arthur Kornberg, then in the microbiology department at Washington University in St. Louis, Missouri, recognized the paper’s significance. Consequently, he became interested in how the body synthesizes nucleic acids—in particular, DNA. During these studies, working with the relatively simple bacterium Escherichia coli, in 1956 he discovered the enzyme that assembles the building blocks of DNA. This enzyme, called DNA polymerase I, is present with some variation in every living organism. Kornberg’s papers describing these findings were initially rejected but later accepted and published in 1957 in the prestigious Journal of Biological Chemistry. In 1959, he was a co-recipient of the Nobel Prize for determining “mechanisms in the biological synthesis of DNA.”

BIOLOGICAL COPY MACHINE

The discovery of DNA polymerase I, commonly designated pol I, is highly significant in biology because it plays a central role in the process of life by contributing to our understanding of how DNA is replicated and repaired. Prior to cell division, pol I duplicates the entire contents of a cell’s DNA. This is followed by the parent cell passing one copy of its DNA to each daughter cell; thus, genetic information is transferred from one generation to the next. Kornberg found that pol I reads an intact DNA strand and uses it as a template to synthesize a new strand, which is identical to the original strand—a process not unlike a copying machine generating duplicate documents.

There are seven subclasses of DNA polymerase (model shown). Some, such as pol I, engage in quality control—reading, detecting, and correcting errors in DNA prior to making a copy.

However, unlike a copy machine that blindly copies the document regardless of its contents, some members of the seven subclasses of DNA polymerases—such as pol I—have the ability to proofread the original DNA template, detecting, removing, and correcting errors, thereby producing a new error-free DNA strand. Other DNA polymerases merely replicate but do not repair, thus perpetuating mutations in the genome or leading to the possible death of the cell.