Chemical Modification of Pseudouridylic Acid in Valine Transfer Ribonucleic Acid I from Torulopsis utilis with a Radioactive Carbodiimide

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Chemical modification of pseudouridylic acid in tRNA^val₁ from Torulopsis utilis was studied with [¹⁴C] N-cyclohexyl-N'-β-(4-methylmorpholinium) ethylcarbodiimide iodide (CMC). After the modified tRNA having 10.6 moles of CMC, obtained from a frac-tionation on DEAE-cellulose, was incubated in 0.02M carbonate buffer (pH 10.3) for 3 hr at 37°C, the tRNA having 3 moles of CMC was obtained. The results of analyses of the tRNA having 3 moles of CMC showed that_??_in C-_??_-U-Ip, T-_??_-C-Gp, U-C-_??_-A-Gp and C-A-_??_-C-U-Gp were modified and the ratios of moles of the modified oligonucleotides to mole of tRNA were 0.45, 0.38, 0.58 and 0.53 respectively. Both tRNA's having 10.6 and 3 moles of CMC could not accept valine. Patterns of absorb-ance-temperature profile and ORD of the tRNA having 3 moles of CMC partially resembled to that of native tRNA in the same phosphate buffer. But the patterns of the tRNA having 10.6 moles of CMC suggested the destraction of the conformation of the tRNA.