5 public questions tagged with this topic.
RNA splicing removes non-coding introns from pre-mRNA and joins the exons to form mature mRNA.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Post-Transcriptional Modifications - Capping Splicing Polyadenylation
Bacterial ribosomal operons rarely harbor introns due to genome streamlining and rapid replication pressure favoring compactness. In contrast, archaeal and eukaryotic rRNA genes, including nuclear 28S and 18S, mitochondrial and chloroplast rRNAs, frequently contain Group I self-splicing introns located at highly conserved core regions. These introns are co-transcriptionally removed by self-splicing assisted by proteins, restoring functional rRNA. Distribution reflects ancestral intron richness in early life and selective loss in bacteria, while archaea and eukaryotes retained mobile intronic e
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 8, Distribution of rRNA introns in archaea and eukaryotes
Mobile or homing introns are self-splicing Group I or Group II introns containing open reading frames encoding homing endonucleases, often belonging to LAGLIDADG or HNH families, and sometimes combined maturase-endonuclease functions. Homing endonuclease introduces site-specific double-strand break in intron-less allele, stimulating homologous recombination repair using intron-containing genome as donor, thereby duplicating intron into new allele. This selfish element drives super-Mendelian inheritance, spreads despite fitness cost, and links splicing to DNA mobility. This refined regulation s
Ref: Watson Molecular Biology of the Gene, 7th ed., Chapter 15, Homing introns encoding homing endonucleases
Introns are intervening sequences interspersed between exons within transcription unit, transcribed into precursor RNA but excised during nuclear processing. Detected as discontinuities between genomic DNA and cDNA, introns vary from few base pairs to hundreds of kilobases, typically beginning GU and ending AG in mammals. Group I, II, and spliceosomal introns removed by different mechanisms; spliceosomal introns excised via lariat formation catalyzed by U1, U2, U5 snRNPs. Though non-coding, introns harbor regulatory RNAs, influence mRNA export, nonsense-mediated decay, and alternative splicing
Ref: Lodish Molecular Cell Biology Chapter 9: Introns intervening sequences definition splicing; Alberts Chapter 6 Intron lariat removal
Eukaryotic protein-coding genes often contain non-coding intervening sequences interrupting coding potential. Philip Sharp and Richard Roberts discovered split gene organization in adenovirus and cellular genes, revealing primary transcripts contain introns removed by spliceosome. Interrupted or split gene refers to locus where exons encoding mature mRNA segments are separated by intronic DNA that is transcribed but excised. This architecture permits alternative splicing, exon shuffling and regulatory intronic elements. Bacterial genes generally lack introns, making split genes hallmark of nuc
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 7: Split Genes and Intervening Sequences, Sharp and Roberts
