TY - JOUR
T1 - Manipulation of the vsg co-transposed region increases expression-site switching in Trypanosoma brucei
AU - Davies, Kelvin P.
AU - Carruthers, Vern B.
AU - Cross, George A.M.
N1 - Funding Information:
This work was supported by the National Institutes of Health (grants AI 21531 and AI 21729). We thank Christine Clayton, Piet Borst and Gloria Rudenko for supplying plasmids, and several colleagues for their comments on this work. Sequencing was performed at the Rockefeller University Shared Technology Center.
PY - 1997/6
Y1 - 1997/6
N2 - Disruption of a region of DNA in Trypanosoma brucei immediately upstream of the expressed telomere-proximal variant surface glycoprotein gene (vsg), known as the co-transposed region (CTR), can cause a dramatic increase in the rate at which the active expression site (ES) is switched off and a new ES is switched on. Deletion of most of the CTR in two ESs caused a greater than 100-fold increase in the rate of ES switching, to about 1.3 x 10-4 per generation. A more dramatic effect was observed when the entire CTR and the 5' coding region of the expressed vsg221 were deleted. In this case a new ES was activated within a few cell divisions. This switch also occurred in cell lines where a second vsg had been inserted into the ES, prior to CTR deletion. These cell lines, which stably co-expressed the inserted and endogenous Vsgs, in equal amounts, did not differ from the wild type in growth rate or switching frequency, suggesting that simultaneous expression of two Vsgs has no intrinsic effect. CTR deletion did not disturb the inserted vsg117. We tentatively conclude that it was not the disruption of the vsg221 in itself that destabilized the ES. All of the observed switches occurred without additional detectable DNA rearrangements in the switched ES. Deletion of the 70-bp repeats and/or a vsg pseudogene upstream of the CTR did not affect ES stability. Several speculative interpretations of these observation are offered, the most intriguing of which is that the CTR plays some role in modulating chromatin conformation at an ES.
AB - Disruption of a region of DNA in Trypanosoma brucei immediately upstream of the expressed telomere-proximal variant surface glycoprotein gene (vsg), known as the co-transposed region (CTR), can cause a dramatic increase in the rate at which the active expression site (ES) is switched off and a new ES is switched on. Deletion of most of the CTR in two ESs caused a greater than 100-fold increase in the rate of ES switching, to about 1.3 x 10-4 per generation. A more dramatic effect was observed when the entire CTR and the 5' coding region of the expressed vsg221 were deleted. In this case a new ES was activated within a few cell divisions. This switch also occurred in cell lines where a second vsg had been inserted into the ES, prior to CTR deletion. These cell lines, which stably co-expressed the inserted and endogenous Vsgs, in equal amounts, did not differ from the wild type in growth rate or switching frequency, suggesting that simultaneous expression of two Vsgs has no intrinsic effect. CTR deletion did not disturb the inserted vsg117. We tentatively conclude that it was not the disruption of the vsg221 in itself that destabilized the ES. All of the observed switches occurred without additional detectable DNA rearrangements in the switched ES. Deletion of the 70-bp repeats and/or a vsg pseudogene upstream of the CTR did not affect ES stability. Several speculative interpretations of these observation are offered, the most intriguing of which is that the CTR plays some role in modulating chromatin conformation at an ES.
KW - Antigenic variation
KW - Expression site
KW - Trypanosoma brucei
KW - Variant surface glycoprotein
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U2 - 10.1016/S0166-6851(97)02853-3
DO - 10.1016/S0166-6851(97)02853-3
M3 - Article
C2 - 9200123
AN - SCOPUS:0030911625
SN - 0166-6851
VL - 86
SP - 163
EP - 177
JO - Molecular and Biochemical Parasitology
JF - Molecular and Biochemical Parasitology
IS - 2
ER -