If you introduced a mutation in region 4 and prevented it from forming a hairpin

Question

If you introduced a mutation in region 4 and prevented it from forming a hairpin with region 3, what type of response would you expect from this mutant E. coli strain?

a) Transcription is terminated at the trp operon attenuator only at high concentration of Trp

b) Transcription is terminated at the trp operon attenuator only at low concentration of Trp

c) Transcription is always terminated at the trp operon attenuator at both high and low concentrations of Trp

d) Transcription is not terminated at the trp operon attenuator at any concentration of Trp

a high tryptophan leader peptide coding region b low tryptophan leader peptide trp operon mRNA tryptophan codons C no protein synthesis Copyright 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Explanation / Answer

ANS:

a) Transcription is terminated at the trp operon attenuator only at high concentration of Trp

Explanation:

In mutations Trp opern's Trptophone levels became low, in low Trp level transcription will continues

A mutation in region 4 and prevented it from forming a hairpin with region 3, can continuously produce the past pairing anti termination signal of Region II with Region III. So the trancription will never stop in low concentration of Trptophone. It always terminate in high Trptophone concentration.

Attenuation: It is a secondary level of the regulation that depends upon the presence or absence of tryptophane.

Attenuation Mechanism: Pairing of Region I with Region II produce pause signal, pairing of Region II with Region III produce anti termination signal and pairing of Region III with Region IV produce termination.

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