Demonstration of G . U wobble base pairs by Raman and IR spectroscopy.

When guanine and uracil form hydrogen bonds in the pairing scheme first proposed by Crick one would expect that poly(A,G) will form an unperturbed double helix with poly U at room temperature in a dilute electrolyte solution (0.1 M NaCl). We have demonstrated by Raman- and IR-spectroscopy that the secondary structure of poly(A.G) . poly U is very similar to the structure of poly A . poly U; only the thermal stability of the double helix seems slightly lower than the stability of poly A . poly U, whereas the average helix length is unaffected by the dispersed G . U base pairs. From our input ratio of guanine and adenine we estimate that about every fourth base pair is a wobble pair.