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#splicing

8 public questions tagged with this topic.

Sex determination-l

In Drosophila, the default splicing pathway is:

In Drosophila alternative splicing hierarchy defaults to male mode when Sex-lethal inactive. Absence of Sxl allows transcripts of Sxl itself to retain exon 3 with premature termination producing no protein, transformer pre-mRNA splices to truncated nonfunctional male form, and doublesex retains male-specific exon producing DsxM driving male differentiation and courtship behaviors. This default splicing requires no activator, occurring constitutively unless Sxl redirects spliceosome by binding intronic repressor elements. Hence XY males display male splicing pathway as ground state, while females actively divert splicing via Sxl and Tra to female isoforms.

Ref: Alberts, Molecular Biology of the Cell, Chapter 8: Default male splicing in Drosophila sex determination.

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Processing of rRNA and tRNA

Group II intron splicing forms

Group II introns share mechanistic ancestry with spliceosomes, forming lariat structure rather than linear product. First step uses internal bulged adenosine within intron domain VI as nucleophile; its 2' OH attacks 5' splice site, generating branched intermediate where intron 5' end linked via 2'-5' phosphodiester to branch point, forming loop. Second step, 5' exon attacks 3' splice site, ligating exons and releasing lariat intron. This lariat pathway underpins evolution of spliceosomal snRNA-mediated splicing in eukaryotic nuclei. This refined regulation supports accurate ribosomal assembly, quality control and translational fidelity under diverse physiological conditions and growth states.

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 8, Group II intron lariat formation via branch-point adenosine

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Processing of rRNA and tRNA

Group I intron is released as

Following two consecutive transesterifications, Group I intron is released as linear molecule carrying exogenous guanosine at its 5' terminus added during first step. The product is not branched because nucleophile is external, not internal branch adenosine. Linear intron may subsequently undergo circularization reactions. Ligated exons join via canonical 3'-5' phosphodiester bond to yield functional mRNA, rRNA or tRNA. Reaction underscores energy-independent splicing using RNA structure itself for catalysis, classic ribozyme chemistry characterized in Tetrahymena rRNA intron. This refined regulation supports accurate ribosomal assembly, quality control and translational fidelity under diverse physiological conditions and growth states.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 6, Linear excision product of Group I introns

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Processing of rRNA and tRNA

Group I intron splicing requires

Group I introns are self-splicing ribozymes catalyzing their own excision via two transesterification steps that require external guanosine cofactor. Free guanosine or GMP, GDP, GTP binds specific G-binding pocket in P7 paired region of intron tertiary structure. Its 3' hydroxyl serves as nucleophile attacking 5' splice site, becoming covalently attached to intron 5' end, freeing upstream exon. Second attack by upstream exon 3' OH on 3' splice site ligates exons. No ATP hydrolyzed, reversible, aided in vivo by maturases. This refined regulation supports accurate ribosomal assembly, quality control and translational fidelity under diverse physiological conditions and growth states.

Ref: Watson Molecular Biology of the Gene, 7th ed., Chapter 15, Group I intron self-splicing requiring external guanosine

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Processing of rRNA and tRNA

tRNA intron splicing is

Eukaryotic and archaeal pre-tRNAs often carry intervening sequences in anticodon loop between positions 37 and 38. Unlike spliceosomal or self-splicing introns, tRNA intron excision requires protein enzymes: heterotetrameric tRNA splicing endonuclease TSEN complex makes two precise cuts excising intron, generating 5' and 3' halves with unusual cyclic phosphate termini. Subsequent healing by kinase, phosphodiesterase and ligase activity (RtcB or Trl1) rejoins exons using ATP. This enzyme-mediated pathway occurs in nucleus and distinguishes tRNA splicing from Group I self-splicing. This refined regulation supports accurate ribosomal assembly, quality control and translational fidelity under diverse physiological conditions and growth states.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 6, Eukaryotic tRNA splicing by TSEN endonuclease complex

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Acid, Base, pH

Eukaryotic mRNAs are generally

monocistronic is the scientifically accurate answer to this question. Within the study of Acid, Base, pH, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of monocistronic directly address what is being asked. Among the other options, polycistronic, overlapping, and non-coding do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.

Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 2

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