Genes of the protozoan parasite Babesia bovis that rearrange to produce RNA species with different sequences.

We describe a highly polymorphic gene family from the protozoan parasite Babesia bovis that encodes a complex pattern of transcripts. Gene rearrangements at this locus (designated BabR ) have generated RNA species that differ in sequence. The naturally occurring virulent field isolate Kv expresses two different sized transcripts that are identical in sequence at their 5' ends but different at the 3' ends. An avirulent derivative of this isolate, Ka, expresses not only these two transcripts but a third, of intermediate size. Analysis of cloned genomic fragments from Ka identified genes encoding all three transcripts. Two fragments contained tandemly repeated copies of the BabR genes. The gene encoding the intermediate sized transcript has undergone a rearrangement, substituting a 5' region different to that shared by the other transcripts. These results suggest that sequence diversity may play an important role in the biological function of the BabR locus.