Mechanisms of suppression in Drosophila. IV. Specificity and properties of tyrosyl-tRNA synthetase.

Tyrosyl-tRNA synthetase from wide type Drosophila can distinguish tRNATyr of wild type from that of the suppressor mutant, su(s)2. The method of fractionation of the enzyme on DEAE-cellulose can produce three different forms of the enzyme. One of these forms is characterized in this study. We describe the apparent Km for K+, Mg2+, ATP, tyrosine and tRNA, as well as its heat stability and molecular weight. Spermine does not replace Mg2+ but is inhibitory, a Ki of 1 mM was obtained. Inhibition by p-chloromercuribenzoate results in a Ki of 1 muM. The properties of tyrosyl-tRNA synthetase of Drosophila are compared to the properties of this enzyme from E. coli, B. subtilis and yeast.