InterPro domain: IPR006027

This domain is found in a number of functionally different proteins:

• NusB a prokaryotic transcription factor involved in antitermination
• TIM44, the mitochondrial inner membrane translocase subunit
• RsmB, the 16S rRNA m5C967 methyltransferase

NusB is a prokaryotic transcription factor involved in antitermination processes, during which it interacts with the boxA portion of the mRNA nut site. Previous studies have shown that NusB exhibits an all-helical fold, and that the protein from Escherichia coli forms monomers, while Mycobacterium tuberculosis NusB is a dimer. The functional significance of NusB dimerization is unknown. An N-terminal arginine-rich sequence is the probable RNA binding site, exhibiting aromatic residues as potential stacking partners for the RNA bases. The RNA binding region is hidden in the subunit interface of dimeric NusB proteins, such as NusB from M. tuberculosis, suggesting that such dimers have to undergo a considerable conformational change or dissociate for engagement with RNA. In certain organisms, dimerization may be employed to package NusB in an inactive form until recruitment into antitermination complexes [ 1 , 2 ].

The antitermination proteins of E. coli are recruited in the replication cycle of Bacteriophage lambda, where they play an important role in switching from the lysogenic to the lytic cycle.

1. Solution structure of the antitermination protein NusB of Escherichia coli: a novel all-helical fold for an RNA-binding protein. EMBO J. 17, 4092-100
2. Crystal structures of the antitermination factor NusB from Thermotoga maritima and implications for RNA binding. Biochem. J. 383, 419-28