The 5′–3′ exonuclease activity of U7 snRNP that degrades the DCP substrate. (A) Nucleotide sequence of the two modified substrates, DCP/1xM and DCP/3xD, that were used to analyze 5′–3′ exonuclease activity of U7 snRNP. The arrows indicate the length of intermediates if the activity stalls after encountering modified nucleotides. (B–E) Degradation of the DCP/1xM and DCP/3xD RNA substrates by either mouse nuclear extract (NE) or recombinant U7 snRNP consisting of the indicated components. The arrows and vertical bars indicate products that accumulate during degradation of the DCP RNA by endogenous or recombinant U7 snRNP. X indicates a product of a nonspecific nucleolytic activity present in the extract. (F) Sequencing-type gel electrophoresis to determine the length of products generated during degradation of DCP/3xD RNA by recombinant U7 snRNP containing indicated components. The ladder of nonspecific degradation products present in the same samples served as size markers.
