There are five common subunits in all three RNA Polymerases

Rpb5

Rpb6

Rpb8

Rpb10

Rpb12

TLS Online TPP Program

#Id: 6780

#Unit 3. Fundamental Processes

The mechanism of spacer sequence acquisition is as 

Each new spacer sequence is inserted next to the leader sequence, with the consequence that the array is a temporal record of acquisitions past. The sequence destined to become spacer is, within the phage genome, known as a “proto-spacer” and lies adjacent to a PAM sequence

TLS Online TPP Program

#Id: 6781

#Unit 3. Fundamental Processes

A set of conserved protein-coding genes is tightly associated with the CRISPR sequences. The two most highly conserved members (cas1 and cas2, for “CRISPR associated”) are found in all cases

TLS Online TPP Program

#Id: 6782

#Unit 3. Fundamental Processes

The protospacer adjacent motif (or PAM for short) is a short DNA sequence (usually 2-6 base pairs in length) that follows the DNA region targeted for cleavage by the CRISPR system, such as CRISPR-Cas9. The PAM is required for a Cas nuclease to cut and is generally found 3-4 nucleotides downstream from the cut site

TLS Online TPP Program

#Id: 6783

#Unit 3. Fundamental Processes

cas1, cas2, and cas4 required to create protospacer sequences Cas1 is  integrase, whereas Cas2 is a ribonuclease. In contrast, of other Cas proteins, Cas6 is involved in expression and processing of the CRISPR cluster and Cas3 in the interference of viral infection.

TLS Online TPP Program

#Id: 6784

#Unit 3. Fundamental Processes

The promoter from which expression is initiated is located within the leader region and generates a single RNA transcript called the pre-crRNA.  In the case of E. coli, the CRISPR is associated with eight cas genes, the products of five of which form a complex called Cascade.

TLS Online TPP Program

#Id: 6785

#Unit 3. Fundamental Processes

crRNA and Cascade are then directed to and cleave the target DNA with the help of Cas3 in E.coli