What are group I and group II introns?

Group I introns are ribozymes found in bacteria, bacteriophages and eukaryotic organellar and nuclear genomes. Group II introns are ribozymes found in bacteria, archaea, and eukaryotic organelles.

What are introns in RNA splicing?

Introns are noncoding sections of an RNA transcript, or the DNA encoding it, that are spliced out before the RNA molecule is translated into a protein. The sections of DNA (or RNA) that code for proteins are called exons.

Are group I introns ribozymes?

Group I introns are large self-splicing ribozymes. They catalyze their own excision from mRNA, tRNA and rRNA precursors in a wide range of organisms.

What is meant by ribozyme?

Ribozymes are catalytically active RNA molecules or RNA–protein complexes, in which solely the RNA provides catalytic activity. The term ribozyme refers to the enzymatic activity and ribonucleic acid nature at the same time. Ribozymes are found in the genomes of species from all kingdoms of life.

Are Group 2 introns ribozymes?

Group II introns are mobile ribozymes that self-splice from precursor RNAs to yield excised intron lariat RNAs, which then invade new genomic DNA sites by reverse splicing.

What are group I and group II introns and where are they different from other introns?

Altogether, these elements are found in all three domains of life: group I introns are present in bacteria, bacteriophages and eukaryotes (organellar and nuclear genomes), while group II introns are present in bacteria, archaea and eukaryotic organelles.

How are introns spliced?

Introns are removed from primary transcripts by cleavage at conserved sequences called splice sites. These sites are found at the 5′ and 3′ ends of introns. Most commonly, the RNA sequence that is removed begins with the dinucleotide GU at its 5′ end, and ends with AG at its 3′ end.

What are introns in DNA?

An intron is a region that resides within a gene but does not remain in the final mature mRNA molecule following transcription of that gene and does not code for amino acids that make up the protein encoded by that gene. Most protein-coding genes in the human genome consist of exons and introns.

Is a self-splicing intron a ribozyme?

The Tetrahymena intron has been the prototypical ribozyme in the study of the splicing pathway. Self-splicing depends on two consecutive transesterification reactions initiated by a nucleophilic attack of the 3′OH of an exogenous guanosine cofactor (exoG) at the 5′ splice site (SS) (Figure 1B).

What types of biochemical reactions does a group 1 intron ribozyme catalyze?

Group I intron RNAs are ribozymes that catalyze two consecutive trans-esterification reactions to excise themselves from the precursor RNAs and ligate the flanking exons together (1).

How does Group II intron RNA catalyze its own splicing?

The group II intron RNA catalyzes its own splicing via transesterification reactions that are the same as those of spliceosomal introns, yielding spliced exons and an excised intron lariat RNA.

What are Group II intron ribozymes?

Griffin EA Jr., Qin Z, Michels WJ Jr., Pyle AM. 1995. Group II intron ribozymes that cleave DNA and RNA linkages with similar efficiency, and lack contacts with substrate 2′-hydroxyl groups. Chem Biol 2: 761–770.

What is the relationship between intron RNA and intron ribozymes?

Group II intron ribozymes and IEPs function together as RNPs, with each IEP binding specifically to the intron RNA that encodes it. As a result, the intron RNAs and IEPs have coevolved over long times to form phylogenetic lineages of mobile introns (Fontaine et al. 1997; Toor et al. 2001).

How do Group II ribozymes catalyze their own splicing reactions?

Group II ribozymes catalyze their own splicing via two sequential transesterification reactions (Fig. 4 A). In the first step, the 2′ OH of the bulged A in DVI acts as the nucleophile to attack the 5′-splice site, producing an intron lariat/3′-exon intermediate.