A selected RNA (isolate 6) efficiently catalyzes a self-capping reacti
on with free GDP, yielding the same 5'-capped structure as is formed b
y protein GTP:RNA guanylyltransferase. This unexplored RNA-catalyzed r
eaction type involving nucleophilic attack on phosphate by phosphate a
dds to the variety of possible postsynthetic RNA-catalyzed RNA modific
ations. The selected RNA requires only Ca2+ for activation and has a b
road active pH range of 4.5-9.0, The RNA also has a 5'-pyrophosphatase
activity.