Molecular and Biochemical Parasitology 92 (1998) 313 – 324 Control mechanisms of the H2A genes expression in Trypanosoma cruzi 1 Concepcio ´n Maran ˜o ´n a , Concepcio ´ n Puerta 2,a , Carlos Alonso b , Manuel C. Lo ´ pez a, * a Instituto de Parasitologı ´a y Biomedicina ‘Lo ´pez Neyra’, Consejo Superior de Inestigaciones Cientı ´ficas, Calle Ventanilla 11, 18001 Granada, Spain. b Centro de Biologı ´a Molecular ‘Seero Ochoa’, Consejo Superior de Inestigaciones Cientı ´ficas -Uniersidad Auto ´noma de Madrid, Canto Blanco, 20049 Madrid, Spain. Received 9 October 1997; accepted 18 December 1997 Abstract In a previous report we have described that the T. cruzi histone H2A gene is encoded in two independent gene clusters located in a single chromosome. In the present paper we show that both gene cluster are actively transcribed as two sized classes of polyadenylated mRNAs demonstrating, moreover, the existence of alternative splicing sites and microheterogeneities at the polyadenylation site. We also describe that while the expression of the H2A genes in the non replicative trypomastigote forms is only residual, in the replicative forms there is constitutive transcription of these genes and that the transcription is not associated to DNA replication. The data show, moreover, that in the replicative forms the steady state levels of the H2A mRNAs are controlled at a post-transcriptional level which is associated to DNA replication. © 1998 Elsevier Science B.V. All rights reserved. Keywords: H2A; T. cruzi ; Transcription; DNA replication; Insertion sequence Abbreiations: DTT, dithiothreitol; DRF, dihydrofolate re- ductase-thymidylate synthase; EDTA, ethylendiamine te- traacetic acid; EGTA, ethyleneglycol-bis-( -amino-ethylether)- N,N,N,N,-tetraacetic acid; HEPES, (N-{2-Hydrox- yethyl}piperazine-N-{2-ethanesulfonic acid}); nt, nucleodide; PCR, polymerase chain reaction; PMSF, phenylmethylsulfonyl fluoride; SDS, sodium dodecyl sulfate; UTR, untraslated region. * Corresponding author. Tel.: +58 805190; fax: +58 203323; e-mail: arce1@ipb.csic.es 1 Note : The nucleotide sequence data reported in this paper are available in the EMBL, GeneBank™ and DDJB data base under the accession number Y13985. 2 Present address: Departamento de Microbiologı ´a y Para- sitologı ´a, Universidad Javeriana, Bogota ´, Colombia. 1. Introduction The Trypanosomatidae nuclear chromatin is or- ganized in nucleosomes constituting approxi- mately 200 bp of DNA associated with four proteins which share biochemical characteristics similar to the histones H2A, H2B, H3 and H4 from higher eukaryotes [1]. The basic structure of the nucleosomes, as they are found in higher organisms, is also maintained in Trypanosomati - 0166-6851/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII S0166-6851(98)00003-6