FB2025_05 , released December 11, 2025

General Information
Term	group_II_intron	ID (Ontology)	SO:0000603 (Sequence Ontology)
Definition	Group II introns are found in rRNA, tRNA and mRNA of organelles in fungi, plants and protists, and also in mRNA in bacteria. They are large self-splicing ribozymes and have 6 structural domains (usually designated dI to dVI). A subset of group II introns also encode essential splicing proteins in intronic ORFs. The length of these introns can therefore be up to 3kb. Splicing occurs in almost identical fashion to nuclear pre-mRNA splicing with two transesterification steps. The 2' hydroxyl of a bulged adenosine in domain VI attacks the 5' splice site, followed by nucleophilic attack on the 3' splice site by the 3' OH of the upstream exon. Protein machinery is required for splicing in vivo, and long range intron to intron and intron-exon interactions are important for splice site positioning. Group II introns are further sub-classified into groups IIA and IIB which differ in splice site consensus, distance of bulged A from 3' splice site, some tertiary interactions, and intronic ORF phylogeny.
Also Known As	"group II intron"
Comment
Links to External Ontologies
	SO.org
Annotations
Records annotated with this term OR any of its CHILD TERMS
No relevant records available
Records annotated with this exact term (annotations to child terms are NOT included)
No relevant records available
Full annotation statements including this term (annotations to child terms are NOT included), and relevant FlyBase records
No relevant statements available

General Information

Term

group_II_intron

ID (Ontology)

SO:0000603 (Sequence Ontology)

Definition

Group II introns are found in rRNA, tRNA and mRNA of organelles in fungi, plants and protists, and also in mRNA in bacteria. They are large self-splicing ribozymes and have 6 structural domains (usually designated dI to dVI). A subset of group II introns also encode essential splicing proteins in intronic ORFs. The length of these introns can therefore be up to 3kb. Splicing occurs in almost identical fashion to nuclear pre-mRNA splicing with two transesterification steps. The 2' hydroxyl of a bulged adenosine in domain VI attacks the 5' splice site, followed by nucleophilic attack on the 3' splice site by the 3' OH of the upstream exon. Protein machinery is required for splicing in vivo, and long range intron to intron and intron-exon interactions are important for splice site positioning. Group II introns are further sub-classified into groups IIA and IIB which differ in splice site consensus, distance of bulged A from 3' splice site, some tertiary interactions, and intronic ORF phylogeny.

Also Known As

"group II intron"

Comment

Links to External Ontologies

SO.org

Annotations

Records annotated with this term OR any of its CHILD TERMS

Full annotation statements including this term (annotations to child terms are NOT included), and relevant FlyBase records

No relevant statements available

Spanning Tree View Settings
Parents/Children View Depth	Show hierarchy levels: for parents, for children
Relationships
Is a	autocatalytically_spliced_intron
Part of
Synonyms & Secondary IDs
Synonyms
	"group II intron" EXACT
Secondary IDs

External Crossreferences & Linkouts
	http://en.wikipedia.org/wiki/Group_II_intron "wiki"

Spanning Tree View Settings

Parents/Children
View Depth

Relationships

Is a

autocatalytically_spliced_intron

Part of

Synonyms & Secondary IDs

Synonyms

"group II intron" EXACT

Secondary IDs

External Crossreferences & Linkouts

http://en.wikipedia.org/wiki/Group_II_intron "wiki"