Group I catalytic intron

[3] First an exogenous guanosine or guanosine nucleotide (exoG) docks onto the active G-binding site located in P7, and then its 3'-OH is aligned to attack the phosphodiester bond at the "upstream" (closer to the 5' end) splice site located in P1, resulting in a free 3'-OH group at the upstream exon and the exoG being attached to the 5' end of the intron.

Then the terminal G (omega G) of the intron swaps out the exoG and occupies the G-binding site, preparing the second ester-transfer reaction: the 3'-OH group of the upstream exon in P1 is aligned to attack the downstream splice site in P10, leading to the ligation of the adjacent upstream and downstream exons and release of the catalytic intron.

[6] Since the early 1990s, scientists started to study how the group I intron achieves its native structure in vitro, and some mechanisms of RNA folding have been appreciated thus far.

A few RNA binding proteins and chaperones have been shown to promote the folding of group I introns in vitro and in bacteria by stabilizing the native intermediates, and by destabilizing the non-native structures, respectively.

No biological role has been identified for group I introns thus far except for splicing of themselves from the precursor to prevent the death of the host that they live by.

A 3D representation of the Group I catalytic intron. This view shows the active site in the crystal structure of the Tetrahymena ribozyme. [ 7 ]
A 3D representation of the Group I catalytic intron. This is the crystal structure of a phage Twort group I ribozyme-product complex. [ 8 ]
A 3D representation of the Group I catalytic intron. This is the structure of the Tetrahymena ribozyme with a base triple sandwich and metal ion at the active site. [ 9 ]