The Wing of the Enhancer-Binding Domain of Mu Phage Transposase is Flexible and is Essential for Efficient Transposition

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 93; no. 3; pp. 1146 - 1150
• Main Authors: Clubb, Robert T., Mizuuchi, Michiyo, Huth, Jeffrey R., Omichinski, James G., Savilahti, Harri, Mizuuchi, Kiyoshi, Clore, G. Marius, Gronenborn, Angela M.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 06.02.1996; National Acad Sciences; National Academy of Sciences
• Subjects: Bacteriophage mu; Bacteriophage mu - enzymology; Binding Sites; Biochemistry; Computer Graphics; Deoxyribonucleic acid; DNA; DNA Nucleotidyltransferases - chemistry; DNA Nucleotidyltransferases - metabolism; DNA, Viral - chemistry; DNA, Viral - metabolism; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - metabolism; Enhancer Elements, Genetic; Gels; Genetic mutation; Genetic transposition; Genomes; Helix-Loop-Helix Motifs; Kinetics; Magnetic Resonance Spectroscopy; Mathematics; Models, Molecular; Mutagenesis, Site-Directed; phage Mu; Protein Structure, Secondary; Proteins; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; Restriction Mapping; Spectral energy distribution; Transposases; Transposons
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.93.3.1146

A tetramer of the Mu transposase (MuA) pairs the recombination sites, cleaves the donor DNA, and joins these ends to a target DNA by strand transfer. Juxtaposition of the recombination sites is accomplished by the assembly of a stable synaptic complex of MuA protein and Mu DNA. This initial critical step is facilitated by the transient binding of the N-terminal domain of MuA to an enhancer DNA element within the Mu genome (called the internal activation sequence, IAS). Recently we solved the three-dimensional solution structure of the enhancer-binding domain of Mu phage transposase (residues 1-76, MuA76) and proposed a model for its interaction with the IAS element. Site-directed mutagenesis coupled with an in vitro transposition assay has been used to assess the validity of the model. We have identified five residues on the surface of MuA that are crucial for stable synaptic complex formation but dispensable for subsequent events in transposition. These mutations are located in the loop (wing) structure and recognition helix of the MuA76 domain of the transposase and do not seriously perturb the structure of the domain. Furthermore, in order to understand the dynamic behavior of the MuA76 domain prior to stable synaptic complex formation, we have measured heteronuclear 15N relaxation rates for the unbound MuA76 domain. In the DNA free state the backbone atoms of the helix-turn-helix motif are generally immobilized whereas the residues in the wing are highly flexible on the pico- to nanosecond time scale. Together these studies define the surface of MuA required for enhancement of transposition in vitro and suggest that a flexible loop in the MuA protein required for DNA recognition may become structurally ordered only upon DNA binding.