novel relaxase homologue is involved in chromosomal DNA processing for type IV secretion in Neisseria gonorrhoeae

• Published in: Molecular microbiology 2007-11, Vol.66 (4), p.930-947
• Main Authors: Salgado-Pabón, Wilmara, Jain, Samta, Turner, Nicholas, van der Does, Chris, Dillard, Joseph P
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Amino Acid Substitution; Bacteria; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Biological and medical sciences; Biological Transport; Chromosomes; Chromosomes, Bacterial - genetics; Chromosomes, Bacterial - metabolism; Deoxyribonucleases - metabolism; Deoxyribonucleic acid; DNA; DNA Helicases - chemistry; DNA Helicases - genetics; DNA Helicases - metabolism; DNA, Bacterial - genetics; DNA, Bacterial - metabolism; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial; Genes; Membranes; Microbiology; Miscellaneous; Molecular biology; Molecular Sequence Data; Mutagenesis, Site-Directed; Mutation; Neisseria gonorrhoeae; Neisseria gonorrhoeae - enzymology; Neisseria gonorrhoeae - genetics; Neisseria gonorrhoeae - metabolism; Transformation, Bacterial
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/j.1365-2958.2007.05966.x

The Neisseria gonorrhoeae type IV secretion system secretes chromosomal DNA that acts in natural transformation. To examine the mechanism of DNA processing for secretion, we made mutations in the putative relaxase gene traI and used nucleases to characterize the secreted DNA. The nuclease experiments demonstrated that the secreted DNA is single-stranded and blocked at the 5' end. Mutation of traI identified Tyr⁹³ as required for DNA secretion, while substitution of Tyr²⁰¹ resulted in intermediate levels of DNA secretion. TraI exhibits features of relaxases, but also has features that are absent in previously characterized relaxases, including an HD phosphohydrolase domain and an N-terminal hydrophobic region. The HD domain residue Asp¹²⁰ was required for wild-type levels of DNA secretion. Subcellular localization studies demonstrated that the TraI N-terminal region promotes membrane interaction. We propose that Tyr⁹³ initiates DNA processing and Tyr²⁰¹ is required for termination or acts in DNA binding. Disruption of an inverted-repeat sequence eliminated DNA secretion, suggesting that this sequence may serve as the origin of transfer for chromosomal DNA secretion. The TraI domain architecture, although not previously described, is present in 53 uncharacterized proteins, suggesting that the mechanism of TraI function is a widespread process for DNA donation.