Abstract
Analysis of the Gram-positive Clostridium acetobutylicum genome reveals an inexplicable level of redundancy for the genes putatively involved in asparagine (Asn) and Asn-tRNA(Asn) synthesis. Besides a duplicated set of gatCAB tRNA-dependent amidotransferase genes, there is a triplication of aspartyl-tRNA synthetase genes and a duplication of asparagine synthetase B genes. This genomic landscape leads to the suspicion of the incoherent simultaneous use of the direct and indirect pathways of Asn and Asn-tRNA(Asn) formation. Through a combination of biochemical and genetic approaches, we show that C. acetobutylicum forms Asn and Asn-tRNA(Asn) by tRNA-dependent amidation. We demonstrate that an entire transamidation pathway composed of aspartyl-tRNA synthetase and one set of GatCAB genes is organized as an operon under the control of a tRNA(Asn)-dependent T-box riboswitch. Finally, our results suggest that this exceptional gene redundancy might be interconnected to control tRNA-dependent Asn synthesis, which in turn might be involved in controlling the metabolic switch from acidogenesis to solventogenesis in C. acetobutylicum.
Highlights
Clostridium acetobutylicum synthesizes asparagine (Asn) and Asn-tRNAAsn
We demonstrate that an entire transamidation pathway composed of aspartyl-tRNA synthetase and one set of GatCAB genes is organized as an operon under the control of a tRNAAsn-dependent T-box riboswitch
Our results suggest that this exceptional gene redundancy might be interconnected to control tRNA-dependent Asn synthesis, which in turn might be involved in controlling the metabolic switch from acidogenesis to solventogenesis in C. acetobutylicum
Summary
Clostridium acetobutylicum synthesizes asparagine (Asn) and Asn-tRNAAsn. Results: Synthesis of Asn is tRNA-dependent and regulated by a T-box riboswitch that is functional in a Gram-negative environment. Besides a duplicated set of gatCAB tRNA-dependent amidotransferase genes, there is a triplication of aspartyl-tRNA synthetase genes and a duplication of asparagine synthetase B genes. This genomic landscape leads to the suspicion of the incoherent simultaneous use of the direct and indirect pathways of Asn and AsntRNAAsn formation. We demonstrate that an entire transamidation pathway composed of aspartyl-tRNA synthetase and one set of GatCAB genes is organized as an operon under the control of a tRNAAsn-dependent T-box riboswitch. Our results suggest that this exceptional gene redundancy might be interconnected to control tRNA-dependent Asn synthesis, which in turn might be involved in controlling the metabolic switch from acidogenesis to solventogenesis in C. acetobutylicum
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