Characterization of a relatively rare class B, type 2 trypanosome variant surface glycoprotein gene.

The variant surface glycoprotein (VSG) gene of Trypanosoma brucei rhodesiense LouTat 1.5, a defined African trypanosome variant antigenic type, was cloned and sequenced. Southern blot analysis revealed 2 DNA restriction fragments in both VSG 1.5 expressor and nonexpressor populations, suggesting that there are 2 genomic copies of the VSG 1.5 gene and no expression-linked copies. Pulsed-field gel electrophoresis followed by Southern blot analysis showed that each copy of the VSG 1.5 gene exists on a separate large chromosome in both the expressor (approximately 3.5- and 4-megabase (Mb) chromosomes) and nonexpressor (approximately 4- and 5.7-Mb chromosomes) populations. Thus, VSG genes may be present on larger chromosomes than previously reported. Sequence analysis and alignments revealed that the VSG 1.5 molecule is a class B VSG with 12 cysteine residues in the N-terminus and is classified as a type 2 VSG based on C-terminus motifs. This classification shows that the VSG 1.5 molecule represents a relatively rare VSG class and type. Taken together, these studies provide additional information on VSG genes and proteins and supply the foundation for structure-function analysis of the VSG 1.5 surface antigen expressed by trypanosomes of the LouTat 1 serodeme.