The ubiquitin-ligase system in Trypanosoma brucei brucei.

The question of whether the African trypanosome Trypanosoma brucei brucei utilizes a ubiquitin-ligase system to conjugate the 8,500-dalton protein ubiquitin to other proteins has not been investigated. Using 125I-labeled ubiquitin and gel electrophoresis (sodium dodecyl sulfate and acetic acid, urea, Triton X-100), we looked for the incorporation of label into proteins larger than ubiquitin to determine ubiquitin-ligase system activity in cytosolic and nuclear lysates of long slender, intermediate, and short stumpy bloodstream-form trypanosomes. We present data suggesting that there is cytosolic activity of a ubiquitin-ligase system in all three bloodstream forms of T. brucei brucei. There are indications that the three bloodstream forms of T. brucei brucei differ in their cytosolic ubiquitin-ligase system activity. Our assay showed no activity of this system in the nucleus of T. brucei brucei. Further studies on the ubiquitin-ligase system in T. brucei brucei may define differences between the three bloodstream forms, the parasite, and its host, leading to development of novel chemotherapeutic strategies.