摘要: Abstract We have studied the involvement of 5' cap structure in splicing precursor mRNAs a HeLa nuclear extract. We show that are spliced efficiently only when they possess and preincubation extract rendered reaction highly sensitive to inhibition by analogues. This sensitization was dependent on exogenous Mg2+ but not ATP or GTP. These results demonstrate is structure, as demonstrated for process whole-cell [Konarska, M. M., Padget, R. A. & Sharp, P. (1984) Cell 38, 731-736], thus support contention recognition an important feature eukaryotic mRNA biogenesis.