ANTISENSE 2'-O-METHYLOLIGORIBONUCLEOTIDES HYBRIDIZED TO RNA BLOCK A NUCLEAR, ATP-DEPENDENT 3'-5' EXONUCLEASE

RNA hybridized to 2'-O-methyloligoribonucleotides and incubated in nuc lear extracts from HeLa cells is truncated, resulting in a distinct pr oduct terminated at the 5' end of the antisense oligonucleotide. The a ctivity responsible for this effect is not RNase H but rather a novel exonuclease degrading RNA in the 3' to 5' direction. The enzyme requir es ATP and Mg2+ ions. Except for dATP, no other nucleoside triphosphat e or nonhydrolyzable ATP analog supports the exonucleolytic activity, In spite of the nuclear origin and activity requirements similar to th ose required for pre-mRNA splicing, the exonuclease operates with equa l efficiency on intron-containing and intronless RNAs, excluding the p ossibility that it is associated with the splicing machinery.