Restricted fragmentation of poliovirus type 1, 2 and 3 RNAs by ribonuclease III.

Cleavage of the genome RNAs of poliovirus type 1, 2 and 3 with the ribonuclease III of Escherichia coli has been investigated with the following results: (1) at or above physiological salt concentration, the RNAs are completely resistant to the action of the enzyme, an observation suggesting that the RNAs lack “primary cleavage sites”; (2) lowering the salt concentration to 0.1 m or below allows RNase III to cleave the RNAs at “secondary sites”. Both large and small fragments can be obtained in a reproducible manner depending on salt conditions chosen for cleavage. Fingerprints of three large fragments of poliovirus type 2 RNA show that they originate from unique segments and represent most if not all sequences of the genome. Based upon binding to poly(U) filters of poly(A)- linked fragments, a physical map of the large fragments of poliovirus type 2 RNA was constructed. The data suggest that RNase III cleavage of single-stranded RNA provides a useful method to fragment the RNA for further studies.