title: The selenocysteine tRNA gene in leishmania major is transcribed by both RNA polymerase II and RNA polymerase III.
abstract: Eukaryotic tRNAs, transcribed by RNA polymerase III (Pol III), contain boxes A and B as internal promoter elements. One exception is the selenocysteine (Sec) tRNA (tRNA-Sec), whose transcription is directed by an internal box B and three extragenic sequences in vertebrates. Here we report on the transcriptional analysis of the tRNA-Sec gene in the protozoan parasite Leishmania major. This organism has unusual mechanisms of gene expression, including Pol II polycistronic transcription and maturation of mRNAs by trans splicing, a process that attaches a 39-nucleotide miniexon to the 5' end of all the mRNAs. In L. major, tRNA-Sec is encoded by a single gene inserted into a Pol II polycistronic unit, in contrast to most tRNAs, which are clustered at the boundaries of polycistronic units. 5' rapid amplification of cDNA ends and reverse transcription-PCR experiments showed that some tRNA-Sec transcripts contain the miniexon at the 5' end and a poly(A) tail at the 3' end, indicating that the tRNA-Sec gene is polycistronically transcribed by Pol II and processed by trans splicing and polyadenylation, as was recently reported for the tRNA-Sec genes in the related parasite Trypanosoma brucei. However, nuclear run-on assays with RNA polymerase inhibitors and with cells that were previously UV irradiated showed that the tRNA-Sec gene in L. major is also transcribed by Pol III. Thus, our results indicate that RNA polymerase specificity in Leishmania is not absolute in vivo, as has recently been found in other eukaryotes.
authors.affiliation: Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla, Estado de México, Mexico Posgrado en Ciencias Biológicas, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla, Estado de México, Mexico.
authors.forename: Norma E
authors.initials: NE
authors.lastname: Padilla-Mejía
authors.affiliation: Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla, Estado de México, Mexico.
authors.forename: Luis E
authors.initials: LE
authors.lastname: Florencio-Martínez
authors.affiliation: Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla, Estado de México, Mexico Posgrado en Ciencias Biológicas, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla, Estado de México, Mexico.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Moreno-Campos
authors.affiliation: Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla, Estado de México, Mexico Posgrado en Ciencias Biológicas, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla, Estado de México, Mexico.
authors.forename: Juan C
authors.initials: JC
authors.lastname: Vizuet-de-Rueda
authors.affiliation: Departamento de Biología Molecular y Biotecnología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Mexico City, Mexico.
authors.forename: Ana M
authors.initials: AM
authors.lastname: Cevallos
authors.affiliation: Departamento de Biomedicina Molecular, Centro de Investigación y de Estudios Avanzados del IPN, Mexico City, Mexico.
authors.forename: Rosaura
authors.initials: R
authors.lastname: Hernández-Rivas
authors.affiliation: Departamento de Biomedicina Molecular, Centro de Investigación y de Estudios Avanzados del IPN, Mexico City, Mexico.
authors.forename: Rebeca
authors.initials: R
authors.lastname: Manning-Cela
authors.affiliation: Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla, Estado de México, Mexico Posgrado en Ciencias Biológicas, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla, Estado de México, Mexico scalv@campus.iztacala.unam.mx.
authors.forename: Santiago
authors.initials: S
authors.lastname: Martínez-Calvillo
mesh_terms: D018320:Leishmania major / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D026723:Polyadenylation; D015800:Protozoan Proteins / Q000378:metabolism*; D012319:RNA Polymerase II / Q000378:metabolism*; D012320:RNA Polymerase III / Q000378:metabolism*; D012326:RNA Splicing; D012346:RNA, Transfer, Amino Acyl / Q000235:genetics*
chemical_list: D015800:Protozoan Proteins; D012346:RNA, Transfer, Amino Acyl; C112705:selenocysteinyl-tRNA; D012319:RNA Polymerase II; D012320:RNA Polymerase III