ABSTRACT
The stages of eukaryotic messenger RNA metabolism include promotion, elongation, capping and methylation of the 5′ end, modification of internal bases, polyadenylation of the 3′ end, splicing, transport to the cytoplasm, association with ribosomes and translation, loss of poly (A), and degradation. Processing of primary transcripts into messenger RNAs should be regarded as a collective strategy for extracting information from the genome and regulating its expression. The distinctive properties of eukaryotes and their mRNAs, as compared to prokaryotes, include:
Covalent splicing of most eukaryotic mRNAs, with preservation of 5′- and 3′-terminal sequences and some internal segments of the primary transcript and deletion of intervening sequences
Transportation of RNAs from their sites of synthesis and processing in the nucleus to their site of translation on the cytoplasmic ribosomes, in contrast to the coupled transcription-translation of prokaryotic mRNAs
The longer lifetimes of eukaryotic messages conferred by capping 5′ ends and poly-adenylating 3′ ends
The selective translation of only the 5′ proximal- open reading frame of most eukaryotic mRNAs, including those which are physically polycistronic, in contrast to the functional polycistrony of prokaryotic mRNAs
The dramatically higher genomic complexity of eukaryotes
The differentiated gene expression of eukaryotes with respect to developmental stage and cell type.
