title: DNA phosphorothioation in Streptomyces lividans: mutational analysis of the dnd locus.
abstract: BACKGROUND
  A novel DNA phosphorothioate modification (DNA sulfur modification), in which one of the non-bridging oxygen atoms in the phosphodiester bond linking DNA nucleotides is exchanged by sulphur, was found to be genetically determined by dnd or dnd-counterpart loci in a wide spectrum of bacteria from diverse habitats. A detailed mutational analysis of the individual genes within the dnd locus in Streptomyces lividans responsible for DNA phosphorothioation was performed and is described here. It should be of great help for the mechanistic study of this intriguing system.
  
  
  RESULTS
  A 6,665-bp DNA region carrying just five ORFs (dndA-E) was defined as the sole determinant for modification of the DNA backbone in S. lividans to form phosphorothioate. This provides a diagnostically reliable and easily assayable Dnd (DNA degradation) phenotype. While dndA is clearly transcribed independently, dndB-E constitute an operon, as revealed by RT-PCR analysis. An efficient mutation-integration-complementation system was developed to allow for detailed functional analysis of these dnd genes. The Dnd- phenotype caused by specific in-frame deletion of the dndA, C, D, and E genes or the enhanced Dnd phenotype resulting from in-frame deletion of dndB could be restored by expression vectors carrying the corresponding dnd genes. Interestingly, overdosage of DndC or DndD, but not other Dnd proteins, in vivo was found to be detrimental to cell viability.
  
  
  CONCLUSIONS
  DNA phosphorothioation is a multi-enzymatic and highly coordinated process controlled by five dnd genes. Overexpression of some proteins in vivo prevented growth of host strain, suggesting that expression of the gene cluster is strictly regulated in the native host.
authors.affiliation: Laboratory of Microbial Metabolism, and School of Life Sciences & Biotechnology, Shanghai Jiaotong University, Shanghai, PR China. tiegangxu@gmail.com
authors.forename: Tiegang
authors.initials: T
authors.lastname: Xu
authors.forename: Jingdan
authors.initials: J
authors.lastname: Liang
authors.forename: Shi
authors.initials: S
authors.lastname: Chen
authors.forename: Lianrong
authors.initials: L
authors.lastname: Wang
authors.forename: Xinyi
authors.initials: X
authors.lastname: He
authors.forename: Delin
authors.initials: D
authors.lastname: You
authors.forename: Zhijun
authors.initials: Z
authors.lastname: Wang
authors.forename: Aiying
authors.initials: A
authors.lastname: Li
authors.forename: Zhongli
authors.initials: Z
authors.lastname: Xu
authors.forename: Xiufen
authors.initials: X
authors.lastname: Zhou
authors.forename: Zixin
authors.initials: Z
authors.lastname: Deng
mesh_terms: D004252:DNA Mutational Analysis; D004269:DNA, Bacterial / Q000378:metabolism*; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D050296:Microbial Viability; D005810:Multigene Family; D016366:Open Reading Frames; D009876:Operon; D010641:Phenotype; D010766:Phosphorylation; D048170:Streptomyces lividans / Q000235:genetics* / Q000378:metabolism
chemical_list: D004269:DNA, Bacterial