Final answer:
The statement that sequences 2 and 3 associating in the trp operon's leader sequence leads to transcription termination is false; instead, this association prevents termination by forming an antiterminator loop.
Step-by-step explanation:
In the mechanism of transcription attenuation of the trp operon, the association between the different sequences of the leader sequence can either terminate transcription or allow it to continue. In this context, it is false that the interaction of sequences 2 and 3 causes premature termination of transcription. Rather, when tryptophan levels are low, the antiterminator loop between sequences 2 and 3 forms, preventing the formation of the terminator loop between sequences 3 and 4 that would normally lead to termination of transcription.
The terminator stem-loop that leads to transcription termination actually forms between sequences 3 and 4 when tryptophan levels are high and the leader peptide is translated smoothly, allowing transcription to halt before the structural genes of the trp operon are transcribed.