Deoxyribonucleic acid methylases in normal and polyoma-virus-transformed BHK-21 cells [proceedings].

when complexed with GTP binds any aminoacyl-tRNA formed and prevents its hydrolysis (Leder, 1973). An average of 0.97mol of tRNAIIe was charged per mol of ATP added to the reaction mix. It may be calculated from the relative reactivity of the isoleucyl-tRNA synthetase towards valine and isoleucine in the presence of tRNA and ATP (Fersht, 1977) and the relative concentrations of valine and isoleucine in the cell (Raunio & Rosenquist, 1970), that 1 mol of ATP is wastefully hydrolysed in rejecting valine for every 16mol of isoleucyl-tRNA successfully charged. Only 6% of the ATP is 'spent' on editing. This is the most costly situation. For the valyl-tRNA synthetase, only 1 mol of ATP is hydrolysed in rejecting threonine for about 13OOmol of valyl-tRNA formed. The overall cost of editing is thus very low.