In molecular biology, antitermination is the prokaryotic cell's aid to fix premature termination during the transcription of RNA.
The sites responsible for determining leftward and rightward antitermination are described as nutL and nutG, respectively.
When pN recognizes the nut site, it forms a persistent antitermination complex in cooperation with a number of E. coli host proteins.
The complex must act on RNA polymerase to ensure that the enzyme can no longer respond to the terminator.
The assembly of NusB, S10, and NusG onto the core complex involves nt 2 to 7 of lambda BOXA (CGCUCUUACACA), as well as the carboxyl-terminal region of N, which interacts with RNAP.
The possibility that RfaH and NusG are redundant for N antitermination has not yet been tested, although for several other functions, the two proteins are not interchangeable.
put sites act in cis to promote readthrough of downstream terminators in the absence of all HK022 proteins.
This prediction is supported by mutational studies and the pattern of sensitivity of the two RNAs to cleavage with single- and double-strand-specific endoribonucleases.
Like lambda N and Q, the PUT sequences suppress polymerase pausing and promote processive antitermination in a purified in vitro transcription system.
The only mutations known to block PUT-mediated antitermination change highly conserved amino acids located in a cysteine-rich amino-proximal domain of the RNAP beta' subunit.
The phage-restricted phenotypes conferred by these mutations suggest that they alter a domain of RNAP-beta’ that interacts specifically with nascent PUT RNA in the transcription elongation complex, but this idea has not been directly tested.
The stability of the putative PUT-RNAP interaction and the nature of the PUT-induced modification to the elongation complex are unknown.
The sequences of the rrn BOXA sites are more similar to the bacteriophage consensus than is that of lambda, and they bind NusB-S10 more efficiently.
Although stem-loop structures analogous to BOXB are found promoter proximal to the BOXA sites, they are not essential for antitermination.
An rrn BOXA sequence confers full antitermination activity against Rho-dependent but not against intrinsic terminators.
A role for NusA is further suggested by the observation that the nusA10 (Cs) mutation inhibits both antitermination and the rate of transcription elongation in an rrn operon.