Nucleic Acids Research, 1990, Vol. 18, No. 24 7219-7227
© 1990
Articles |
Duplicative activation mechanisms of two trypanosome telomeric VSG genes with structurally simple 5' flanks
Institute of Genetics and Wellcome Unit of Molecular Parasitology, Glasgow University Church street, Glasgow G11 5JS, UK
*To whom correspondence should be addressed
Received October 23, 1990. Revised November 26, 1990. Accepted November 26, 1990.
In the mammalian bloodstream, African trypanosomes express variant surface glycoprotein (VSG) genes from a family of long and complex telomeric expression sites. VSG switching generally occurs by the duplication of different VSG genes into these sites by gene conversion involving a series of 70 base pair (70bp) repeats in the 5' flank. In contrast, when VSG is first synthesised by trypanosomes in the tsetse fly at the metacyclic stage, a separate set of telomeric expression sites is activated. These latter telomeres appear not to act as recipients in gene conversion. We have found that the structure of two such expression sites is simple, with very short 70bp repeat regions and very little other sequence in common with bloodstream expression sites. However, the two telomeres readily act as donors in VSG gene conversion in the bloodstream and we show for one a consistent association of the conversion 5' end point with the short 70bp repeat region. These findings help explain why a very predictable set of VSGs is expressed in the tsetse fly and have implications for VSG gene conversion mechanisms.
Present address: +Department of Internal Medicine, Yale MacArthur Center for Molecular Parasitology, Yale University School of Medicine, New Haven, CN, USA
Present address: 
Division of Molecular Biology, The Netherlands Cancer Institute (Antoni van Leeuwenhoek Huis) Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
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