Final answer:
Attenuation is a biological process where transcription is prematurely terminated to regulate gene expression based on the needs of the cell. In the context of the His operon and other operons related to amino acid biosynthesis, the process generally relies on the coupled system of transcription and translation in bacteria. However, the underlying mechanism involves the availability of charged tRNA, which can still cause attenuation in the absence of translation.
Step-by-step explanation:
Attenuation is a regulatory mechanism by which bacteria can rapidly adjust the expression of certain genes in response to environmental conditions. This process specifically refers to the premature termination of transcription, ensuring that a gene or set of genes is only expressed when its products are required by the cell. In the case of the His operon, which is related to histidine biosynthesis, attenuation is closely linked to the coupling of transcription and translation, a characteristic feature of prokaryotic gene expression. Here, ribosomes begin translating the RNA transcript almost as soon as it is produced by RNA polymerase.
However, in scenarios where translation is absent, the question is how attenuation could function without this coupling. The key lies in understanding that the feedback mechanism is typically reliant on the levels of certain charged tRNA molecules which match the amino acid being produced by the operon. In the His operon, for example, when histidine is abundant, the charged tRNA for histidine is also plentiful. This allows for the successful translation of a leader peptide, which forms a specific structure in the RNA that induces transcription termination before the full operative genes are transcribed.