Two distinct selection processes are required:

 • Positive selection, which selects for those thymocytes bearing receptors capable of binding self-MHC molecules, resulting in MHC restriction

• Negative selection, which selects against thymocytes bearing high-affinity receptors for self-MHC/peptide complexes, resulting in self-tolerance.

TLS Online TPP Program

#Id: 614

#Unit 2. Cellular Organization

Attenuation is primarily based on riboswitch (Leader sequence) that function in co-translationally in trp operon

TLS Online TPP Program

#Id: 615

#Unit 2. Cellular Organization

Attenuator riboswitch (Leader sequence) is made up of almost 140 nt which further can be divided into four Intra -complementary regions 

TLS Online TPP Program

#Id: 616

#Unit 2. Cellular Organization

Attenuator riboswitch (Leader sequence) contains two major check-points in region 1

1. UGG codons on position 10, 11

2. A stop codon UGA between Region 1 and 2

TLS Online TPP Program

#Id: 617

#Unit 2. Cellular Organization

Attenuator riboswitch (Leader sequence) region 1 is translated atleast till codon 10 and 11 in case of Low trp concentration.

TLS Online TPP Program

#Id: 618

#Unit 2. Cellular Organization

Attenuator riboswitch (Leader sequence) region 1 is translated  till UGA (R1-2) in case of high trp concentration

TLS Online TPP Program

#Id: 619

#Unit 2. Cellular Organization

Region 1 Leader peptide is of 14 Amino acids Met------Ser