Cold adaptation of tRNA nucleotidyltransferases: a tradeoff in activity, stability and fidelity

CCA-adding enzymes are highly specific RNA polymerases that synthesize and maintain the sequence CCA at the tRNA 3‘-end. Here, we investigated the impact of cold adaptation on the reactivity and specificity of CCA-adding enzymes from psychrophilic bacteria. A comparative study of the corresponding enzymes from closely related psychro-, meso-, and thermophilic Bacillales indicates that the cold-adapted enzymes show a considerable error rate during CCA synthesis, resulting in additional incorporations of C and A residues. It seems that the activity of psychrophilic CCA-adding enzymes is not only achieved at the expense of structural stability, reaction velocity and substrate affinity, but also results in a reduced polymerization fidelity. in vivo tRNA from four Bacillales species was isolated from exponential and stationary growth phase each in triplicates resulting in a total of 24 samples. Sequencing libraries were created for small RNA species and sequenced on 3 runs of a MiSeq using 8 indices. Reads were analyzed regarding 3'-ends of tRNA and results summed up as a mean for the 8 conditions investigated. Results from B. subtilis were regarded as reference sample for a mesophilic Bacillales species. Differences towards psychophilic Planococcus halocryophilus and Exiguobacterium sibiricum and thermophilic Geobacills stearothermophilus were investigated.