Question

1. Create a table comparing features of editing by CDAR (C to U), editing by ADAR (A to I) and pan-editing.   

Answer 1

RNA editing refers to post-translational modification of RNA by modification or substitution, insertion or deletion of nucleotides.

	CDAR (C to U) editing	ADAR (A to I) editing	PAN editing
1	Observed in plant mitochondria, chloroplast, mammals including humans. Second important type of editing in mammals.	Observed in viruses, mammals including humans. Most important type of editing in mammals.	Observed in kinetoplastid protozoa, first seen in mitochondria (kinetoplasts) of Trypanosoma. Also, in crypto genes, acanthamoeba t RNA, Physarium.
2	It is based on base modification or substitution.	It is based on base modification or substitution.	It is based on base insertion or deletion.
3	Involves action of Cytidine deaminases.	Involves the action of Adenosine deaminases acting on double stranded (ADAR).	Involves extensive type of editing, compared to simple internal or topical editing.
4	RNA editing converts: Cytidine base (C) is de-aminated to Uridine (U). In humans it is observed in nuclear transcripts encoding intestinal apolipoproteins (like APO B). In APO B, editing converts codon CAA to UAA (stop codon), resulting in altered lipoprotein metabolism.	RNA editing converts: Adenosine (A) to Inosine (I), by hydrolytic de-amination of Adenosine base. Inosine base pairs with cytosine (instead of Uracil), thus changing the transcriptional protein. In humans, observed in receptors of central nervous system, like alteration of properties of ion channels.	RNA editing starts with base pairing using a guide RNA (g RNA) with pre-edited RNA, around insertion/deletion point. The double strand thus created, is surrounded by multiple enzyme complex called editosome. Editosome makes an endonuclease cleavage, and poly U insertion occurs. Insertion takes place in presence of A or G base sequences of g RNA and stops on encountering U or C.