Optical measurements reveal base-pairing in T4-specific mRNAs

Previous studies have shown that 60-70% of the nucleotides in rRNA, tRNA and the RNA of the RNA bacteriophages are involved in base pairing. To determine whether this is also true of mRNAs coded from double-stranded DNA, T4-specific mRNAs were purified using two different techniques: hybridization to T4 DNA or chromatography on benzoylated DEAE-cellulose columns followed by sucrose gradients. We have determined the optical melting curves of the purified mRNAs. The hypochromicities calculated from these melting curves were similar to those of rRNA, indicating comparable amounts of base pairing in rRNA and T4-specific mRNA. If this hypochromicity were due to random base pairing, we would have expected a less sharp melting curve and a lower Tm than for the rRNA controls. On the contrary, the mRNA samples had very high cooperativities and Tm values.