The genomic organization and transcription of the ubiquitin genes of Trypanosoma cruzi

Abstract

We describe here the organization of the ubiquitin genes of the parasitic protozoan Trypanosoma cruzi. T. cruzi contains greater than 100 ubiquitin coding sequences all of which are clustered into a 27 kb segment of the genome. Two types of ubiquitin coding sequences were found. There are five fusion genes (FUS1-5) consisting of a ubiquitin coding sequence fused to a basic non-ubiquitin sequence. The T. cruzi ubiquitin fusion protein is 84% homologous to the product of the UBI gene of Saccharomyces cerevisiae. The non-ubiquitin domains of the two proteins are 67% homologous. There are five polyubiquitin coding genes (PUB) each consisting of varying lengths of polyubiquitin coding sequence and terminating with a single copy of the larger fusion gene. Transcription of the ubiquitin genes results in the generation of six major poly(A)+ mRNAs. The pattern of transcription accurately reflects the genomic organization, in that the transcripts consist of either a single copy of the ubiquitin fusion coding sequence or varying lengths of polyubiquitin (up to 52 copies of the ubiquitin coding unit) each ending with a single copy of the ubiquitin fusion sequence. Finally, there are heat shock elements 5' to the PUB genes and transcription patterns are altered under conditions of stress.