Post-transcriptional modification
Biological processes that chemically alter RNA after transcription.
Post-transcriptional modification is a set of biological processes common to most eukaryotic cells by which an RNA primary transcript is chemically altered following transcription from a gene to produce a mature, functional RNA molecule. These modifications are vital for the correct translation of eukaryotic genomes, as the initial precursor mRNA often contains both exons and introns, and processing steps such as capping, polyadenylation, and splicing are required to produce a functional mRNA that can leave the nucleus.
- field
- Molecular biology
- known_for
- Chemical alteration of RNA after transcription to produce mature, functional RNA
Lore & Background
Post-transcriptional modification includes three major steps for messenger RNA: addition of a 5' cap, addition of a 3' polyadenylated tail, and RNA splicing. The 5' cap involves adding 7-methylguanosine to protect the RNA from ribonucleases. The 3' processing involves cleavage and addition of about 250 adenine residues to form a poly(A) tail, guided by signal sequences such as AAUAAA. RNA splicing removes introns and links exons, catalyzed by the spliceosome.
Reader's Guide
Post-transcriptional modification is significant because it enables eukaryotic cells to produce diverse, functional RNA molecules from a single gene. The 5' cap and poly(A) tail protect mRNA from degradation and facilitate transport to ribosomes. Splicing, including alternative splicing, allows production of many protein variants from limited DNA. These processes are essential for gene expression regulation and are conserved across most eukaryotes. The article notes that modifications also occur for transfer RNA, ribosomal RNA, and other RNA types, and that histone mRNA processing differs by lacking introns and poly(A) tails.
Did You Know?
- The 5' cap is added by removing the terminal phosphate, then adding 7-methylguanosine in a 5'5' triphosphate link.
- Polyadenylation adds about 200 adenine units to the 3' end using ATP as a precursor.
- Alternative splicing allows production of a large variety of proteins from a limited amount of DNA.
- Core histone mRNAs lack poly(A) tails and introns, and their 3' processing uses a stem-loop structure and U7 snRNA.
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