There are two classes of snoRNPs involved in rRNA processing in nucleolus. 

The box H/ACA snoRNPs are involved in pseudouridylylation, and box C/D snoRNPs function in 2-O-methylations.

TLS Online TPP Program

#Id: 789

#Unit 3. Fundamental Processes

Rho factor is an essential protein in E. coli that causes transcription termination, accounts for almost half of E. coli terminators.

TLS Online TPP Program

#Id: 790

#Unit 3. Fundamental Processes

Sequences of Rho dependent transcription termination

1. Rho binds a rut site. 

2. The rho factor then tracks along the RNA until it catches up to RNA polymerase. 

3. When the RNA polymerase reaches the termination site, rho first freezes the structure of the polymerase and then invades the exit channel to destabilize the enzyme, causing it to release the RNA. 

4. Pausing by the polymerase at the site of termination allows time for rho factor to translocate to the hybrid stretch.

TLS Online TPP Program

#Id: 791

#Unit 3. Fundamental Processes

A rut site has a sequence rich in C -41% and poor in G preceding the actual site(s) of termination. The sequence corresponds to the 3’ end of the RNA.

 

TLS Online TPP Program

#Id: 792

#Unit 3. Fundamental Processes

C is by far the most common base (41%) and G is the least common base (14%) in rut sites, vary in length.  As a general rule, the efficiency of a rut site increases with the length of the C-rich/G-poor region.

TLS Online TPP Program

#Id: 793

#Unit 3. Fundamental Processes

Rho is a member of the family of hexameric ATP-dependent helicases. Each subunit has an RNA-binding domain and an ATP hydrolysis domain.

TLS Online TPP Program

#Id: 794

#Unit 3. Fundamental Processes

Rho activity is impeded when ribosomes are translating an mRNA.