Final answer:
Without all steps listed, it's impossible to identify which tRNA processing step is not involved in E. coli from the given information. Additional research would be required to accurately answer the student's question.
Step-by-step explanation:
The question relates to the processing of precursor tRNA molecules in E. coli. tRNA molecules must be processed before they can participate in protein synthesis. The processing steps include trimming, addition of a -C-C-A base triplet at the 3' end, and modification of internal bases. However, the information provided does not list all steps involved in tRNA processing in E. coli, and therefore it is not possible to determine which step is not part of tRNA processing in E. coli solely from the given excerpts. For a more comprehensive understanding, additional sources should be consulted to verify the full sequence of events in the processing of tRNA molecules in prokaryotic cells like E. coli.