Re: How does transcription attenuation cause RNA Polymerase to terminate?

The termination of transcription is of 2 types:
a.	Intrinsic termination caused by formation of hairpin loop of mRNA
b.	Rho dependent termination

The sequence of hairpin loop mRNA is inverted repeat with GC rich region at 
the stem (which increases the strength of the stem). This is followed by 
poly (dA) at termination site. Due to formation of hairpin loop, RNA 
polymerase pauses near the termination site. Also because of poly (dA) 
the DNA-RNA hybrid, which has less strength (AT bond less stable than GC bond),
causes the RNA polymerase to 
detach from DNA resulting in transcription termination. 

Also proteins like Nus in E. coli increase the efficiency of termination 
of transcription. These proteins attach to RNA polymerase. 

The anti-termination occurs when continuous transcription of two adjacent 
genes is essential. Binding of proteins like pN in E. coli to RNA 
polymerase causes anti-termination. The RNA polymerase slides along the 
terminator site without detaching.

Reference:
Genes 7: Benjamin Levin

regards,

Devendra Dusane