The central dogma of molecular biology states that DNA is “transcribed” into RNA, which is then “translated” into protein. Proteins are made by linking together a series of units called amino acids; errors can occur when the information in the RNA is misinterpreted leading to the incorporation of the wrong amino acid. This phenomenon, termed “misreading” is our laboratory’s main interest. A small RNA called a transfer RNA (tRNA) is responsible for decoding the RNA. Our laboratory has developed an enzyme-based reporter system to measure misreading rates. The lacZ gene encoding the enzyme beta-galactosidase was mutated to produce an enzyme lacking significant activity. Misreading of the mutant gene can restore activity. The rate of misreading is equal to the ratio of the mutant enzyme activity to wild type activity. In bacteria, misreading occurs at a rate of about 1 in 1000 to 1 in 10,000. This research seeks to determine what the error rate is in human cells using this system. We propose to insert the lacZ gene from bacterial plasmids into plasmids that can be used in HeLa cells, which are immortal human tissue culture cells. A similar method of misreading analysis will be applied to the human cells’ beta-galactosidase activity in order to understand errors in cell machinery during the process of protein production.