The kinetics of bisulphite modification of reactive residues in E. coli tRNA2Phe.

E coli tRNA2Phe was modified at 25 degrees C with 3M sodium bisulphite, pH6.0, for periods of up to 48 hours, Three cytadinine residues, at position 17, 74 and 75 from the 5' end were each deaminated to uridine. The 2-methylthio-N6-isopentenyl adenosine at position 37 formed a 1:1 bi-sulphite addition product which was stable to alkaii. No other residues were permanently modified. The rate of modification of each residue was first order with respect to remaining unmodified nucleotide, the time of half reaction, t1/2, being different for each residue. C17 reaction reacted at twice the rate of cytidine in PolyC, indicating that it occupied a very exposed position in the tRNA.