 Morpholinos can interfere with pre @-@ mRNA processing steps either by preventing splice @-@ directing small nuclear ribonucleoproteins ( snRNP ) complexes from binding to their targets at the borders of introns on a strand of pre @-@ mRNA , or by blocking the nucleophilic adenine base and preventing it from forming the splice lariat structure , or by interfering with the binding of splice regulatory proteins such as splice silencers and splice enhancers . Preventing the binding of snRNP U1 ( at the donor site ) or U2 / U5 ( at the polypyrimidine moiety and acceptor site ) can cause modified splicing , commonly excluding exons from the mature mRNA . Targeting some splice targets results in intron inclusions , while activation of cryptic splice sites can lead to partial inclusions or exclusions . Targets of U11 / U12 snRNPs can also be blocked . Splice modification can be conveniently assayed by reverse @-@ transcriptase polymerase chain reaction ( RT @-@ PCR ) and is seen as a band shift after gel electrophoresis of RT @-@ PCR products . 
