TETRAMETHYLAMMONIUM DOES NOT UNIVERSALLY NEUTRALIZE SEQUENCE-DEPENDENT DNA STABILITY

Effects of different concentrations of Tetramethylammonium on the ther mostability of six DNA dumbbells with similar well defined sequences h ave been investigated. Each molecule has a 16 base pair duplex stem li nked on both ends by T4 single strand loops. Only the sequence of the four central base pairs distinguishes one molecule from the next. The distinguishing central sequences are, [A-T-A-T], [T-A-T-A], [A-A-A-A], [C-G-C-G], [G-C-G-C] and [G-G-G-G] situated between the sequences: 5' -G-T-A-T-C-C-[]-G-G-A-T-A-C-3' which are the same in all molecules. Op tical melting curves collected on these molecules as a function of TMA concentration over the range from 0.09 M to 4.5 M revealed there is n o single concentration of TMA where all these molecules exhibit the sa me melting temperature.