ADP-ribosyl transferase activity in Trypanosoma brucei

Nuclear adenosine diphosphoribosyl transferase (ADPRT) catalyses the covalent modification of chromatin proteins by (ADP-ribose)n. This activity, which is entirely dependent on DNA containing strand breaks, is required for efficient DNA excision repair possibly because it regulates DNA ligation. ADPRT activity is also required for cytodifferentiation in a number of different cell types. We report here the presence of ADPRT activity in the blood-stream form of Trypanosoma brucei and its activation by DNA strand breaks formed by exposure to, either exogenously supplied deoxyribonuclease I, or treatment with the methylating agent, dimethylsulphate. 3-Aminobenzamide, but not its chemical analogue 3-aminobenzoic acid, is a competitive inhibitor of ADPRT activity in T. brucei. Intact trypanosomes are readily permeable to this competitive inhibitor of ADPRT activity.