During recent years there has been considerable interest in the study of the transfer ribonucleic acids (tRKA), and programs for the separation, purification, and characterization of these compounds are in progress in many laboratories.2 There is an obvious need for accurate and precise analytical data, particularly for the assay of individual, purified, or partiall? purified tRNA's.
Consequently we have begun a critical evaluation of Dhr: available analytical techniques in order to establish the optimum conditions for quantitative determinations. This report describes the determinat#iorr of picomolar quantities of purified phenylalanine-and leucine-accepting tRNA's by aminoacylation using a crude synthetase enzyme preparation. The aminoacylation reaction was first described by Hoagland, Zamecnik, and Stephenson (1). Previous studies of this reaction are reviewed by Brown (2) and Zachau and Feldmann (3). The tRNA is incubated with a 14( 'labeled amino acid and a mixed synthetase preparation, in the presenc*c of ATP and other cofactors, to form a tRNA-amino acid est)er linkage a(*cording to the over-all reaction. tRNA + aa*\ + ATP z tRn'A.aa* + AMP + ppi 'RUBIN, KELMERS, AND CiOtiSTEIN