A REALISTIC VERSION OF THE Y-MODEL FOR DNA DYNAMICS AND SELECTION OF SOLITON SPEED

In the Y model of DNA dynamics [Phys. Lett. A 136 (1989) 413] one assu mes the bases to be all equal; in this note we modify the Y model to a ccount for the differences among bases. We use this ''realistic Y mode l'' to study significant special sequences, and obtain a selection of the speed of solitons - except the simplest, ''elementary'' ones - in DNA; the selected speed is unphysical, suggesting that only the elemen tary solitons are present in real DNA. The obtained results also apply to a purine/pyrimidine approximation for the general case. We also di scuss how cooperative effects could cause the equal bases approximatio n to be better than the purine/pyrimidine one.