title: Diversity of core promoter elements comprising human bidirectional promoters.
abstract: BACKGROUND
  Bidirectional promoters lie between adjacent genes, which are transcribed from opposite strands of DNA. The functional mechanisms underlying the activation of bidirectional promoters are currently uncharacterised. To define the core promoter elements of bidirectional promoters in human, we mapped motifs for TATA, INR, BRE, DPE, INR, as well as CpG-islands.
  
  
  RESULTS
  We found a consistently high correspondence between C+G content, CpG-island presence and an average expression level increasing the median level for all genes in bidirectional promoters. These CpG-rich promoters showed discrete initiation patterns rather than broad regions of transcription initiation, as are typically seen for CpG-island promoters. CpG-islands encompass both TSSs within bidirectional promoters, providing an explanation for the symmetrical co-expression patterns of many of these genes. In contrast, TATA motifs appear to be asymmetrically positioned at one TSS or the other.
  
  
  CONCLUSIONS
  Our findings demonstrate that bidirectional promoters utilize a variety of core promoter elements to initiate transcription. CpG-islands dominate the regulatory landscape of this group of promoters.
authors.affiliation: National Human Genome Research Institute, National Institutes Health, Rockville, MD 20852, USA. yangma@mail.nih.gov
authors.forename: Mary Qu
authors.initials: MQ
authors.lastname: Yang
authors.forename: Laura L
authors.initials: LL
authors.lastname: Elnitski
mesh_terms: D001482:Base Composition; D018899:CpG Islands; D020869:Gene Expression Profiling; D015894:Genome, Human; D006801:Humans; D011401:Promoter Regions, Genetic; D012319:RNA Polymerase II / Q000235:genetics; D016385:TATA Box; D024363:Transcription Initiation Site; D014158:Transcription, Genetic
chemical_list: D012319:RNA Polymerase II