InterPro domain: IPR010995

This superfamily represents an alpha-helical bundle domain, which has a SAM domain-like fold. This compact domain consists of a 4-5 helical bundle of two orthogonally packed alpha-hairpins, and contains one classic and one pseudo HhH (helix-hairpin-helix) motif. This domain is found at N-terminal of the DNA repair protein Rad51, at the C-terminal of the transcription elongation protein NusA, and at the C-terminal of the hypothetical protein AF1548.

Human Rad51 protein is a homologue of Escherichia coli RecA protein, and functions in DNA repair and recombination [ 1 ]. In higher eukaryotes, Rad51 protein is essential for cell viability. The N-terminal region of Rad51 is highly conserved among eukaryotic Rad51 proteins but is absent from RecA, suggesting a Rad51-specific function for this region. The-terminal domain is involved in interactions with DNA and proteins; DNA binding may be regulated via phosphorylation within the N-terminal domain.

NusA (N utilisation substance A) from E. coli is an essential transcription factor that associates with the RNA polymerase (RNAP) core enzyme, where it modulates transcriptional pausing, termination and anti-termination [ 2 ]. The C-terminal of NusA consists of two repeat units, and is responsible for the interaction of NisA with the C-terminal of RNAP, and with its interaction with protein N from phage lambda during anti-termination [ 3 ].

1. The N-terminal domain of the human Rad51 protein binds DNA: structure and a DNA binding surface as revealed by NMR. J. Mol. Biol. 290, 495-504
2. The E. coli NusA carboxy-terminal domains are structurally similar and show specific RNAP- and lambdaN interaction. Protein Sci. 14, 2018-29
3. Structural basis for the interaction of Escherichia coli NusA with protein N of phage lambda. Proc. Natl. Acad. Sci. U.S.A. 101, 13762-7