Biology · Molecular Biology

Following statements were made about the post-transcriptional processing of RNA in eukaryotes: A. Soon after transcription initiation, RNA polymerase II pauses ~30 nucleotides downstream from the site of initiation until the Cap structure is added to the 5' end of the nascent pre-mRNA. B. The 5' splice sites are functionally divergent whereas the 3' sites are functionally equivalent. C. In addition to helping in recognition of the splice sites, the exon definition also functions as a splicing regulator by allowing pairing and linking of adjacent 5' and 3' splice sites. D. The intron definition mechanism applies only to the larger introns (above 500 nucleotides length) and assists in achieving alternate splicing. E. The splicing reactions carried out in vitro have revealed that the first and second transesterification reactions are reversible. Which one of the following combinations of statements is correct?