In Vivo Function of tRNase Z in Esherichia coli and Yeast Saccharomyces cerevisiae

在大多数生物体中，tRNase Z被认为是tRNA分子3‘端加工所必需的。然而，在正常生长条件下，大肠杆菌tRNase ZS基因似乎是必不可少的。在这里，我们在体外密集地研究了各种(前)tRNA作为大肠杆菌tRNase ZS的良好底物，发现这种酶可以从成熟的tRNAs中蚕食3‘端的CCA残基。此外，我们发现，当大肠杆菌tRNase ZS在细胞中充分表达时，通过从氨基酰tRNAs中去除氨基酸来停止生长。目前的数据表明，在某些应激条件下，tRNase ZS可能通过抑制翻译来帮助调节细胞的生长速度。我们还检测了重组酵母tRNase ZL对不同酵母前tRNAs的3‘端加工活性。重组酵母tRNase ZL经识别核苷酸后能有效切割酵母前tRNAs。综上所述，我们推测大肠杆菌和酵母的tRNase Z区结构的不同可能导致了底物识别和切割位点的特异性。

In most organisms, tRNase Z is thought to be essential for 3′ processing of tRNA molecules. The Escherichia coli tRNase ZS gene, however, appears to be dispensable under normal growth conditions. Here we intensively examined various (pre-)tRNAs for good substrates of E. coli tRNase ZS in vitro, and found that the enzyme can nibble off the 3′ terminal CCA residues from mature tRNAs. Furthermore, we discovered that E. coli tRNase ZS, when sufficiently expressed in the cell, shuts down growth by removing amino acids from aminoacyl-tRNAs. The current data suggest that tRNase ZS may help modulate a cell growth rate by repressing translation under some stressful conditions. We also examined 3′ processing activity of recombinant yeast tRNase ZL against various yeast pre-tRNAs in vitro. The recombinant yeast tRNase ZL was able to cleavage yeast pre-tRNAs efficiently after the discriminator nucleotide. Taken together, we speculate the difference of tRNase Z domain structure between E. coli and yeast might lead to the specificity of substrate recognition and cleavage site.