Polygene transcripts are precursors to calmodulin mRNAs in trypanosomes.

In African trypanosomes, calmodulin is encoded by a small family of tandemly repeated genes consisting of three to four units. We show that all the members of the calmodulin cluster of Trypanosoma brucei gambiense are expressed. In addition to mature mRNAs, steady-state RNA contains a small percentage of polygene transcripts which comprise at least two and probably all calmodulin genes. The 5' ends of a portion of these molecules appear to be indistinguishable from those of mature calmodulin mRNAs. Polygene transcripts are not polyadenylated and have discrete ends which map in the intergenic regions downstream from the polyadenylation sites. Using biotinylated hybridization probes and selection of the hybrids on streptavidin-agarose, we further show that calmodulin polygene transcripts are the most abundant RNA species detected in pulse-labelled RNA of cultured procyclic trypanosomes. Our data strongly imply that polygene transcripts are authentic precursors to mature calmodulin mRNAs.