Characterisation of the loci encoding the glutamic acid and alanine rich protein of Trypanosoma congolense

We have characterised the organisation of genes encoding the glutamate and alanine rich protein (GARP) surface coat of the procyclic and epimastigote stages of Trypanosoma congolense in the tsetse fly. The GARP genes are arranged at two, possibly physically linked, loci, one of which exhibits allelic variation. One locus contains a single GARP gene, whilst both alleles of the other have a large tandem array of polycistronically transcribed GARP genes. Sequence analysis has revealed that there are very few coding differences between different GARP genes. A sequence related to the Trypanosoma brucei expression site associated gene 4 (encoding a transmembrane protein with a cytoplasmic adenylate cyclase domain) has been identified within a region at the downstream flank of one locus. There is no evidence that, within the single trypanosome, GARP genes are as diverse as the procyclin genes that encode a corresponding coat in T. brucei.