A Spring-Loaded State of NusG in Its Functional Cycle Is Suggested by X-ray Crystallography and Supported by Site-Directed MutantsKnowlton, J.R., Bubunenko, M., Andrykovitch, M., Guo, W., Routzhan, K.M., Waugh, D.S., Court, D.L., Ji, X.
(2003) Biochemistry 42: 2275-2281
- PubMed: 12600194
- DOI: 10.1021/bi0272508
- Primary Citation of Related Structures:  1NPP
- PubMed Abstract:
- Crystal structures of transcription factor NusG in light of its nucleic acid-and protein-binding activities
Steiner, T.,Kaiser, J.T.,Marinkovic, S.,Huber, R.,Wahl, M.C.
(2002) Embo J. 21: 4641
Transcription factor NusG is present in all prokaryotes, and orthologous proteins have also been identified in yeast and humans. NusG contains a 27-residue KOW motif, found in ribosomal protein L24 where it interacts with rRNA. NusG in Escherichia co ...
Transcription factor NusG is present in all prokaryotes, and orthologous proteins have also been identified in yeast and humans. NusG contains a 27-residue KOW motif, found in ribosomal protein L24 where it interacts with rRNA. NusG in Escherichia coli (EcNusG) is an essential protein and functions as a regulator of Rho-dependent transcription termination, phage lambda N and rRNA transcription antitermination, and phage HK022 Nun termination. Relative to EcNusG, Aquifex aeolicus NusG (AaNusG) and several other bacterial NusG proteins contain a variable insertion sequence of approximately 70 residues in the central region of the molecule. Recently, crystal structures of AaNusG in space groups P2(1) and I222 have been reported; the authors conclude that there are no conserved dimers among the contacting molecules in the crystals [Steiner, T., Kaiser, J. T., Marinkovic, S., Huber, R., and Wahl, M. C. (2002) EMBO J. 21, 4641-4653]. We have independently determined the structures of AaNusG also in two crystal forms, P2(1) and C222(1), and surprisingly found that AaNusG molecules form domain-swapped dimers in both crystals. Additionally, polymerization is also observed in the P2(1) crystal. A unique "ball-and-socket" junction dominates the intermolecular interactions within both oligomers. We believe that this interaction is a clue to the function of the molecule and propose a spring-loaded state in the functional cycle of NusG. The importance of the ball-and-socket junction for the function of NusG is supported by the functional analysis of site-directed mutants.
Macromolecular Crystallography Laboratory, National Cancer Institute, P.O. Box B, Frederick, Maryland 21702, USA.