Mj. Lodes et al., EXPRESSION OF A RETROPOSON-LIKE SEQUENCE UPSTREAM OF THE PUTATIVE TRYPANOSOMA-BRUCEI VARIANT SURFACE GLYCOPROTEIN GENE-EXPRESSION SITE PROMOTER, Molecular and cellular biology, 13(11), 1993, pp. 7036-7044
We have cloned the region spanning the putative promoter from two vari
ant surface glycoprotein gene expression sites that are at each end of
chromosome M4 of Trypanosoma brucei IsTat 7. Both expression sites co
ntain a retroposon-like sequence (ESR) pseudogene whose 3' end is appr
oximately 30 bp upstream of the putative expression site promoter. The
ESRs from both expression sites share considerable sequence homology
and are related to LINE-like elements, especially the T. brucei ingi r
etroposon. Other ESRs are located on large, but not intermediate or mi
ni-, chromosomes in the IsTaR 1 serodeme, and the total copy number is
10 to 20, similar to that estimated for variant surface glycoprotein
expression sites. No DNA rearrangements in the vicinity of the ESR and
putative expression site promoter were detected following antigenic s
witches in the IsTaR 1 serodeme. ESR transcripts are present in bloods
tream, but not procyclic, forms. Variation in transcript size and sequ
ence between bloodstream variant antigenic types implies that only the
ESR from the active expression site is transcribed. This pattern of e
xpression reflects that of sequences downstream of the putative expres
sion site promoter, suggesting that the region of coordinately control
led expression extends upstream of this promoter.