RNA:DNA hybrids are more stable than DNA:DNA duplexes in concentrated perchlorate and trichloroacetate solutions

Rates of formation of RNA:DNA hybrids have been measured as a function of temperature and compared to DNA:RNA duplex denaturation temperatures in 4 M sodium perchlorate, 4 M NaClO4-6 M urea, and 3 M rubidium trichloracetate solvents. The usual bell shaped curves of reaction rate versus temperature were observed. The optimal temperatures for the RNA:DNA association reaction are 5 degrees to 12 degrees greater than the Tm's for DNA:DNA denaturation in these solvents, just as in formamide. R-loops of phi80d3ilv DNA with E. coli rRNA can be formed at high efficiency in these solvents.