Polyribonucleotides Containing a Phosphorothioate Backbone

The enzymatic synthesis of two polyribonucleotides, poly r( s̄ A s̄ U) and poly r( s̄ U) containing a sugar‐phosphorothioate instead of a sugar‐phosphate backbone, is described. The formation and thermal stability of double‐stranded polymers is not impaired by this modification. They can also serve as templates for RNA‐polymerase. Single stranded polymers can serve as messengers. Both double and single‐standed polymer exhibit some degree of resistance to nucleases.