Occurrence of 2'-5' phosphodiester linkages in RNA preparations. III. Formation of 2'-5' phosphodiester linkages in polyribonucleotides.

Unlike technical grade yeast RNA, which was confirmed to contain several per cent of 2'-5' phosphodiester linkages, RNA prepared from different kinds of commercial yeast in a cold room consisted exclusively of 3'-5' phosphodiester linkages. Heat treatment of the 3'-5' linked RNA solution resulted in partial isomerization of the internucleotide linkage of the polynucleotide chain (C3'-C5'→C2'-C5'). The isomerization of RNA occurred in the presence of water, at high temperature, and under acidic conditions. Treatment of dry RNA at 100°C for 2 hr did not result in any detectable isomerization. The isomerization was actually observed in yeast RNA when yeast cells suspended in sodium chloride solution were heated. It is concluded therefore that 2'-5' phosphodiester linkages found in technical grade RNA had been formed neither at a step of precipitating RNA with acid nor at a step of drying RNA, but had been formed at a step of heat extraction of RNA from yeast. When 0.1% poly (A) solution, pH 4.8, was heated for 20 hr in a boiling water bath, the isomerization proceeded during the first 6 hr, and finally reached about 37%, irrespective of chain length.