What occurs in low levels of TRP attenuation?

In low levels of tryptophan (TRP) attenuation, the process primarily involves the continuation of translation due to the absence of tRNA-bound TRP. When TRP concentrations are low, the charges of tRNA with TRP are reduced, meaning there are fewer tRNA molecules available to bring TRP to the ribosome. This situation leads to a stall in the ribosome at the tryptophan codons of the mRNA, allowing for specific sequences to be formed in the mRNA that results in the formation of a leader peptide.

The RNA polymerase can continue transcription as ribosomes stall, allowing the folding of the mRNA that promotes anti-terminator structures. This means the genes that help in synthesizing TRP can continue being translated, resulting in an upregulation in the production of proteins associated with TRP synthesis under low TRP conditions. Thus, the mechanism allows for adaptation to the nutrient availability, ensuring that the organism can synthesize more of the amino acid when it is scarce.