Class III IF proteins- found in cells of mesodermal origin

Desmin, GFAP, vimentin

TLS Online TPP Program

#Id: 558

#Unit 2. Cellular Organization

There are 4 genes (I, Z, Y, A), 2 Promoters and 3 lac operators in Lac operon

The major O1 lac operator lies adjacent to promoter

Two auxiliary O2 and O3 lac operators 

All three operators are required for optimum repression 

TLS Online TPP Program

#Id: 559

#Unit 2. Cellular Organization

The O1 operator extends from position -5 just upstream of the mRNA start point to position +21 within the transcription unit.

TLS Online TPP Program

#Id: 560

#Unit 2. Cellular Organization

When polymerase binding causes transition to the open complex and initiates transcription. This gives a low level of constitutive expression called the basal level. 

Binding of RNA polymerase is the rate-limiting step in this case.

TLS Online TPP Program

#Id: 561

#Unit 2. Cellular Organization

lacZ encodes for b-galactosidase, a tetramer of 500 kD. The enzyme breaks lactose is cleaved into glucose and galactose. This enzyme also produces an important byproduct, b-1,6-allolactase.

TLS Online TPP Program

#Id: 562

#Unit 2. Cellular Organization

The lac mRNA (as most mRNA is in bacteria) is extremely unstable and decays with a half-life of only 3 minutes.

TLS Online TPP Program

#Id: 563

#Unit 2. Cellular Organization

B-1,6-allolactase is a true inducer of Lac operon which activates Lac ZYA gene expression by inhibiting Lac Repressor