1a. Many uridine molecules are inserted into some mitochondrialmRNAs in trypanosomes.  The uridine residues come fromthe poly(U) tail of a donor strand!  Nucleosidetriphosphates do not participate in thisreaction.  Propose a reaction mechanism that accounts forthese findings.  (HINT:  relate this RNAediting to RNA splicing.)
b. Analysis of  p53 gene mutations in human tumorsshows that a large proportion of these mutations involve GC→ATtransitions originating at sites of DNAmethylation.  Propose a model to explain preferentialmutagenesis of this type at these sites.
