| What are ribozymes? | An RNA that has catalytic activity. |
| What is the basis of autosplicing ? | Group I Introns Undertake Self-Splicing by Transesterification
Splicing occurs by two transesterification reactions, without requiring input of energy.
The only factors required for autosplicing (or self-splicing) in vitro by group I introns are two metal ions and a guanosine nucleotide.
Self-splicing occurs by transesterification reactions in which bonds are exchanged directly.
The excised intron can form circles. |
| What is the functions of group I of introns? | Group I introns form a secondary structure with nine duplex regions.
The cores of regions P3, P4, P6, and P7 have catalytic activity.
Group I Introns Undertake Self-Splicing by Transesterification
By changing the substrate binding site of a group I intron, it is possible to introduce alternative sequences that interact with the reactive G.
Mobile introns are able to insert themselves into new sites.
Mobile group I introns encode an endonuclease that makes a double-strand break at a target site.
The intron transposes into the site of the double-strand break by a DNA-mediated replicative mechanism. |
| What is group II introns? | Group II introns can autosplice in vitro but are usually assisted by protein activities encoded in the intron.
A single reading frame specifies a protein with reverse transcriptase activity, maturase activity, a DNA-binding motif, and a DNA endonuclease.
The endonuclease cleaves target DNA to allow insertion of the intron at a new site.
The reverse transcriptase generates a DNA copy of the inserted RNA intron sequence. |
| What is introns homing? | The ability of certain introns to insert themselves into a target DNA.
The reaction is specific for a single target sequence. |
| what is RNA editing? | A change of sequence at the level of RNA following transcription. |
| What is the role guide RNAs in RNA editing? | The substrate RNA base pairs with a guide RNA on both sides of the region to be edited.
The guide RNA provides the template for addition (or less often, deletion) of uridines.
Editing is catalyzed by the editosome, a complex of endonuclease, exonuclease, terminal uridyl transferase activity, and RNA ligase. |
| What is ineins in protein splicing? | An intein has the ability to catalyze its own removal from a protein in such a way that the flanking exteins are connected.
Most inteins have two independent activities: protein splicing and a homing endonuclease. |
| What is exteins in protein splicing? | External pro tein sequences that flank an intein (q.v.) and are ligated during protein splicing (q.v.) to form a mature protein. |
