DNA Pol a/ primase and DNA Pol d (which primarily act on the lagging strand) are only recruited after DNA unwinding.

TLS Online TPP Program

#Id: 6398

#Unit 2. Cellular Organization

Repression-Trp aporepressor dimer binds high tryptophan, changes conformation with high affinity for trp operator

Tryptophan is a corepressor

TLS Online TPP Program

#Id: 6399

#Unit 2. Cellular Organization

trp operon can run even in the presence of repressor. The attenuation system permits another 10-fold control over the operon’s activity.  Thus, the combination of repression and attenuation controls the operon over a 700-fold range, from fully inactive to fully active: (70-fold [repression] X 10-fold [attenuation] = 700-fold). 

TLS Online TPP Program

#Id: 6400

#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: 6401

#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: 6402

#Unit 2. Cellular Organization

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

UGG codons on position 10, 11

A stop codon UGA between Region 1 and 2

TLS Online TPP Program

#Id: 6403

#Unit 2. Cellular Organization

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