A 10 base pair element that is essential for autonomous plasmid replication in procyclic trypanosomes is dispensable in bloodstream‐forms

Abstract

Trypanosoma brucei is a unicellular digenetic parasitic protozoan that alternates between the bloodstream of its mammalian host (bloodstream–forms) and the mid‐gut and salivary glands of its insect vector (procyclic and metacyclic forms respectively). These stages are bio‐chemically distinct.Chromosomal DNA replication is an unexplored aspect of trypanosome biology. We are using an autonomously replicating plasmid as a model system to identify sequences that regulate this fundamental biological process in the parasite. One such element maps to a developmentally modulated procyclin promoter that drives reporter gene transcription on this episome. Linker substitution of a 10 base‐pair segment within Domain III of this promoter reduces reporter gene expression by ~10 fold, but abolishes the ability of this plasmid to replicate in procyclic trypanosomes. The close association of replication and transcription control elements and the interplay between these two processes as the parasite shifts from one developmental stage to another is of interest to us.We now demonstrate that the requirements for the replication of these episomes differ between the two developmental stages of this parasite as the 10 base pair Domain III element is dispensable in bloodstream‐forms. In addition, our results suggest that the procyclin‐promoter on this plasmid does not support reporter gene expression in bloodstream forms. Since there are no other known T. brucei promoters on this episome, it would appear that transcription (and possibly replication) initiates adventitiously on this plasmid in the blood‐stage of this parasite. Promiscuous initiation of transcription and replication may be an interesting feature of trypanosome biology.Funded by William Paterson University SURP and NIH