title: Transcriptional regulation of an iron-inducible gene by differential and alternate promoter entries of multiple Myb proteins in the protozoan parasite Trichomonas vaginalis.
abstract: Iron-inducible transcription of a malic enzyme gene (also reputed to be ap65-1) in Trichomonas vaginalis was previously shown to involve a Myb1 repressor and a Myb2 activator, each of which may preferentially select two closely spaced promoter sites, MRE-1/MRE-2r, which comprises overlapping promoter elements, and MRE-2f. In the present study, an iron-inducible approximately 32-kDa Myb3 nuclear protein was demonstrated to bind only the MRE-1 element. Changes in the iron supply, which produced antagonistic effects on the levels of Myb2 and Myb3 expression, also resulted in temporal and alternate entries of Myb2 and Myb3 into the ap65-1 promoter. Repression or activation of basal and iron-inducible ap65-1 transcription was detected in transfected cells when Myb3 was, respectively, substantially knocked down or overexpressed. In the latter case, increased Myb3 promoter entry was detected with concomitant decrease in Myb2 promoter entry under specific conditions, while Myb3 promoter entry was inhibited under all test conditions in cells overexpressing Myb2. In contrast, concomitant promoter entries by Myb2 and Myb3 diminished in cells overexpressing Myb1, except that Myb3 promoter entry was slightly affected under prolonged iron depletion. Together, these results suggest that Myb2 and Myb3 may coactivate basal and iron-inducible ap65-1 transcription against Myb1 through conditional and competitive promoter entries.
authors.affiliation: Division of Infectious Diseases, Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan, Republic of China.
authors.forename: Hong-Ming
authors.initials: HM
authors.lastname: Hsu
authors.forename: Shiou-Jeng
authors.initials: SJ
authors.lastname: Ong
authors.forename: Ming-Chun
authors.initials: MC
authors.lastname: Lee
authors.forename: Jung-Hsiang
authors.initials: JH
authors.lastname: Tai
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D015815:Cell Adhesion Molecules / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D007501:Iron / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D020626:Oncogene Proteins v-myb / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D014158:Transcription, Genetic; D014246:Trichomonas vaginalis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: C096723:AP65-1 protein, Trichomonas vaginalis; D015815:Cell Adhesion Molecules; D020626:Oncogene Proteins v-myb; D015800:Protozoan Proteins; D007501:Iron