Computer assisted size measurement on a digitising tablet of nucleic acid and protein molecules from gels

A method is presented for the rapid and convenient determination of molecular weight or chain length of macromolecules from their electrophoretic mobility in gels, using a computer-controlled digitising tablet. A novel feature is accurate compensation for ‘smile’ or ‘frown’ profiles as well as for the possible splay or curvature of lanes. A family of monotonic, asymptotic, generalised quadratics is calculated to fit locally the known values in a marker track, and a weighting function is then applied to these enveloping curves so that the prediction algorithm simulates the interpolation of unknown values from a smooth graph drawn through the known bands. Results for double stranded DNA, single and double stranded RNA, and protein molecules are given. The average error of the predicted values against the known molecular sizes was 0.2% for dsDNA, 1.7% for dsRNA, 0.7% for ssRNA and 3.6% for protein molecules.