Expression site associated genes of Trypanosoma brucei rhodesiense

Upstream of at least some telomere-linked genes for the variant surface glycoproteins (VSGs) of African trypanosomes are expression site associated genes (ESAGs) whose transcription is co-ordinated with the transcription of the adjacent VSG gene [Cully et al. (1985) Cell 42, 173-182]. The function of the corresponding ESAG proteins is not known. Here we show the sequences of two members of the ESAG-I family that are upstream of the VSG genes expressed in metacyclic variant antigen types 4 and 7 of Trypanosoma brucei rhodesiense. The corresponding metacyclic ESAG-I proteins of about 330 amino acids display extensive positional identity both with each other and with two other ESAG-I proteins of Trypanosoma brucei brucei. Only about 7% of the positions are occupied by a different amino acid in each of the four putative ESAG proteins while 40% of the positions are identical. Thus, the ESAG-I proteins are much more highly conserved than are the VSGs studied to date.