EXPRESSION OF GARP, A MAJOR SURFACE GLYCOPROTEIN OF TRYPANOSOMA-CONGOLENSE, ON THE SURFACE OF TRYPANOSOMA-BRUCEI - CHARACTERIZATION AND USEAS A SELECTABLE MARKER

Procyclic and epimastigote forms of Trypanosoma congolense express an immunodominant glutamic acid/alanine-rich protein (GARP) that covers t he parasite surface. Although GARP shows no sequence similarity to pro cyclins from T. brucei, the general characteristics of the two sets of surface glycoproteins suggest that they have analogous functions, in much the same way that variant surface glycoproteins with unrelated pr imary sequences fulfil the same function in bloodstream form trypanoso mes. Since T. brucei and T. congolense do not follow the same pathway through the tsetse fly, one possible function of procyclins might be t o direct parasites to the correct compartments. As a first step toward s testing this hypothesis, we have produced stably transformed procycl ic forms of T. brucei in which the GARP coding region has been integra ted into a procyclin expression site. GARP can be detected on the surf ace of these transgenic trypanosomes, uniformly distributed within the endogenous procyclin coat, but there are differences in post-translat ional modification when it is expressed in T. brucei rather than in T. congolense. The fact that GARP is readily accessible to antibodies wh ich were raised against a bacterial fusion protein led us to examine i ts potential as a selectable surface marker for transfection. We have established a rapid and simple procedure for isolating stable transfor mants that provides an alternative to conventional methods of selectio n for antibiotic resistance.