T-box riboswitches are important in detecting the presence of uncharged tRNAs. The tRNA binds its anti-codon to the regulatory region of the mRNA, which is formed of stem-loop structures. If the tRNA is uncharged, its amino acid binding sequence will interact with a second stem-loop structure, modifying the secondary mRNA structure and allowing the expression of the gene.
If the tRNA is charged, it will not be able to interact with the second loop structure. This inability to interact twice with the mRNA prevents the ribosome binding site (RBS) from being exposed, and the protein is not expressed.
By having a mechanism to control the expression of metabolic enzymes, as with the T-box riboswitch, that is dependent on the concentration of the final product, it is possible to maintain homeostatic control of the concentration of product. Having a constant concentration of amino acid is important in allowing the cell to synthesise proteins as needed. As the mRNA transcripts for amino acid synthesis are constantly present, it is possible for the relevant metabolic pathway to be rapidly expressed. This helps to increase the survival chances of the cell.
Different t-box riboswitch sequences will be found for each amino acid, conveying specificity while allowing the concentration of each to be maintained independently.