Discussion
When tryptophan level is low in Escherichia coli, the expression of tryptophan biosynthesis genes is turned on through an antiterminator stem-loop formation between
Answer: B
The antiterminator forms between regions 2 and 3 of the trpL leader.
The trp operon is regulated by attenuation. Region 1 of the leader encodes a short peptide with two tandem tryptophan codons. When tryptophan is scarce, charged tRNATrp is scarce too, and the ribosome stalls on region 1. Region 2 is then free to pair with region 3, forming the antiterminator, which prevents the 3:4 terminator hairpin from forming, so RNA polymerase continues into the structural genes.
When tryptophan is plentiful, the ribosome moves on and covers region 2, so regions 3 and 4 pair to form the terminator and transcription stops. The 1:2 hairpin is the pause structure. Regions 2 and 4 are not complementary partners in this model.
Post your comment
Please log in or register to post a comment.
Examination Categories
- SSC Exams
- Banking Exams
- Teaching Exams
- Civil Services Exams
- Railways Exams
- Engineering Recruitment Exams
- Defence Exams
- State Government Exams
- Police Exams
- Insurance Exams
- Nursing Exams
- Other Government Exams
- NRA CET
- PG Entrance Exams
- Campus Placement
- MBA Entrance Exams
- CUET and UG Entrance
- Judiciary Exams
- Regulatory Body Exams
- Software Development