The Bacillus subtilis tyrZ Gene Encodes a Highly Selective Tyrosyl-tRNA Synthetase and is Regulated by a MarR Regulator and T Box Riboswitch
Misincorporation of d-tyrosine (d-Tyr) into cellular proteins due to mischarging of tRNATyr with d-Tyr by tyrosyl-tRNA synthetase inhibits growth and biofilm formation of Bacillus subtilis. Furthermore, many B. subtilis strains lack a functional gene encoding d-aminoacyl-tRNA deacylase, which prevents misincorporation of d-Tyr in most organisms. B. subtilis has two genes that encode tyrosyl-tRNA synthetase: tyrS is expressed under normal growth conditions, and tyrZ is known to be expressed only when tyrS is inactivated by mutation. We hypothesized that tyrZ encodes an alternate tyrosyl-tRNA synthetase, expression of which allows the cell to grow when d-Tyr is present. We show that TyrZ is more selective for l-Tyr over d-Tyr than is TyrS; however, TyrZ is less efficient overall. We also show that expression of tyrZ is required for growth and biofilm formation in the presence of d-Tyr. Both tyrS and tyrZ are preceded by a T box riboswitch, but tyrZ is found in an operon with ywaE, which is predicted to encode a MarR family transcriptional regulator. Expression of tyrZ is repressed by YwaE and also is regulated at the level of transcription attenuation by the T box riboswitch. We conclude that expression of tyrZ may allow growth when excess d-Tyr is present.
Williams-Wagner, R.N., Grundy, F.J., Raina, M., Ibba, M. and Henkin, T.M. (2015) The Bacillus subtilis tyrZ gene encodes a highly selective tyrosyl-tRNA synthetase and is regulated by a MarR regulator and T box riboswitch. J. Bacteriol. 197, 1624-1631. https://doi.org/10.1128/JB.00008-15
American Society for Microbiology