CHARACTERIZATION OF A TRANSCRIPTION TERMINATOR OF THE PROCYCLIN PARP-A UNIT OF TRYPANOSOMA-BRUCEI

The polycistronic procyclin PARP (for procyclic acidic repetitive prot ein) A transcription unit of Trypanosoma brucei was completely charact erized by the mapping of the termination region. In addition to the ta ndem of procyclin genes and GRESAG 2.1, this 7.5- to 9.5-kb unit conta ined another gene for a putative surface protein, termed FAG (for proc yclin-associated gene) 3. The terminal 3-kb sequence did not contain s ignificant open reading frames and cross-hybridized with the beginning of one or several transcription units specific to the bloodstream for m, At least three separate fragments from the terminal region were abl e to inhibit chloramphenicol acetyltransferase expression when inserte d between either the PARP, the ribosomal, or the variable surface glyc oprotein promoter and a chloramphenicol acetyltransferase reporter gen e. This inhibition was due to an orientation-dependent transcription t ermination caused by the combination of several attenuator elements wi th no obvious sequence conservation. The procyclin transcription termi nator appeared unable to inhibit transcription by polymerase II.