MOLECULAR CHARACTERIZATION AND TRANSCRIPTION OF THE HISTONE H2B GENE FROM THE PROTOZOAN PARASITE TRYPANOSOMA-CRUZI

The structure, genomic organization and transcription of the gene enco ding histone H2B in the protozoan parasite Trypanosoma cruzi have been studied. This gene consists of a 746-nucleotide unit, tandemly repeat ed at least 18 times in each of two clusters. DNA probes corresponding to histones H2B and H3 hybridized to different chromosomes revealing that the genes coding for these two histones are not physically linked in the genome of T. cruzi.The primary transcription product of the H2 B gene is processed by trans-splicing and polyadenylation. Inhibition of DNA synthesis with aphidicolin resulted in the reduction of histone H2B mRNA to undetectable levels in about two hours, suggesting that i ts abundance is regulated throughout the cell cycle as it occurs in ot her eukaryotes. in addition, a concomitant inhibition of translation b y cycloheximide reverted this effect indicating that de novo protein s ynthesis is required for RNA instability. Histone mRNA abundance was d ependent on the life-cycle stage of T. cruzi: abundant in amastigotes and epimastigotes, the dividing forms in the host cell and the insect vector, respectively, while undetected in trypomastigotes, the parasit e's non-dividing life stage.