Antisense 2′-O-Methyloligoribonucleotides Hybridized to RNA Block a Nuclear,ATP-Dependent 3′-5′ Exonuclease

Abstract

RNA hybridized to 2′-O-methyloligoribonucleotides and incubated in nuclear extracts from HeLa cells is truncated, resulting in a distinct product terminated at the 5′ end of the antisense oligonucleotide. The activity responsible for this effect is not RNase H but rather a novel exonuclease degrading RNA in the 3′ to 5′ direction. The enzyme requires ATP and Mg²⁺ ions. Except for dATP, no other nucleoside triphosphate or nonhydrolyzable ATP analog supports the exonucleolytic activity. In spite of the nuclear origin and activity requirements similar to those required for pre-mRNA splicing, the exonuclease operates with equal efficiency on intron-containing and intronless RNAs, excluding the possibility that it is associated with the splicing machinery.