title: Length of thymidine homopolymeric repeats modulates promoter activity of sabA in Helicobacter pylori.
abstract: BACKGROUND
  Helicobacter pylori uses SabA to interact with sialyl-Lewis x on the gastric mucosal surface to establish persistent colonization. The number of CT repeats in sabA is variable and thus influences SabA translation, but the expression of SabA determined by Western blotting does not fully match with a CT sequence-based prediction. Furthermore, a homopolymeric thymidine (polyT) tract located upstream of sabA has been observed, but its role in regulating sabA expression is still unknown.
  
  
  METHODS
  The transcriptional start site (TSS) of sabA in strains J99 and Hp258 was determined by 5' RACE. One hundred and fifteen clinical isolates were sequenced to analyze the distribution of the polyT tract length and promoter sequence. Finally, RT-PCR and an E. coli-lux reporter system were used to determine the sabA promoter activity with different lengths of the polyT tract.
  
  
  RESULTS
  The TSS of sabA was located at 66 or 64 bp upstream of the translational start codon in J99 and Hp258, respectively. The polyT tract close to the -35 element varied from T₁₀ to T₂₈ in 115 clinical isolates, and 70% of the isolates contained a stretch of 14-19 Ts. The sabA gene displayed slipped strand mispairing (SSM) of the polyT tract, generating varying genotypes in J99 (16-18 Ts) and Hp258 (14-15 Ts). Furthermore, J99 with lengths of T₁₆ and T₃₀, had higher sabA promoter activity than the common length of T₁₈.
  
  
  CONCLUSIONS
  Our findings indicate that the sabA promoter region modulates its transcriptional activity through a variable polyT tract, and SSM generates mixed genotypes in the population.
authors.affiliation: Institute of Basic Medical Sciences, College of Medicine, National Cheng-Kung University, Tainan, Taiwan.
authors.forename: Cheng-Yen
authors.initials: CY
authors.lastname: Kao
authors.forename: Shew-Meei
authors.initials: SM
authors.lastname: Sheu
authors.forename: Bor-Shyang
authors.initials: BS
authors.lastname: Sheu
authors.forename: Jiunn-Jong
authors.initials: JJ
authors.lastname: Wu
mesh_terms: D018829:Adhesins, Bacterial / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D015964:Gene Expression Regulation, Bacterial; D016481:Helicobacter Infections / Q000382:microbiology*; D016480:Helicobacter pylori / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D013936:Thymidine / Q000737:chemistry / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D018829:Adhesins, Bacterial; C500808:SabA protein, Helicobacter pylori; D013936:Thymidine