Gene Organization And Promoter Analysis Of Histone Genes In Protozoan Trichomonas Vaginalis

Deep-branching eukaryote Trichomonas vaginalis is a parasitic protozoan which is the major cause of trichomoniasis, an important sexually transmitted disease. Therefore, better understudying of transcriptional regulation mechanisms in T. vaginalis may have potential medical implication. The draft genome sequences of T. vaginalis give us the opportunity to study the gene organization of histones. Genomic analysis revealed that most of histones in T. vaginalis organize as H2A/H2B and H3/H4 gene pairs with head-to-head orientation, which is consistent with the existence of H2A/H2B and H3/H4 functional complexes in vivo. The high number of histones genes encoded in T. vaginalis genome facilitates us to identify the cis-regulatory elements in the 5' upstream regions of histones. Sequence comparison of the 5' upstream sequences of histones in T. vaginalis revealed that most of histones contain three motifs. Beside with the conservation of sequence composition, the positions of three motifs are also highly conserved. In addition, we found that (1) three elements occur predominantly in the promoter regions in the T. vaginalis genome, (2) motif I is highly similar to the Inr, which mediated transcription start site selection in T. vaginalis, (3) of the genes having motif II or motif III in promoter regions, all of possible 25 cell-cycle regulated proteins indicated by annotation information solely have motif II .Those findings indicated three elements identified from promoter regions of histones may function in the gene transcription regulation.