PlsPI

PlsPI, also known as the Plasmid DNA Purification Index, is a metric used in molecular biology to assess the quality of purified plasmid DNA. It is derived from the absorbance readings taken at different wavelengths during a spectrophotometric analysis. Specifically, PlsPI is calculated by dividing the absorbance reading at 260 nanometers (A260) by the absorbance reading at 280 nanometers (A280).

The A260 reading is primarily used to quantify the concentration of nucleic acids, including plasmid DNA. The A280 reading, on the other hand, is affected by the presence of proteins, which absorb strongly at this wavelength. Therefore, the PlsPI ratio provides an indication of protein contamination in the DNA sample. A pure DNA sample will have a PlsPI ratio typically between 1.8 and 2.0. Lower ratios, such as those below 1.8, suggest the presence of protein contamination. Conversely, ratios significantly higher than 2.0 might indicate RNA contamination or other interfering substances. While not a definitive measure of DNA integrity or sequence accuracy, PlsPI is a quick and commonly used initial assessment of DNA purity following purification protocols.