A strand bias occurs in point mutations associated with variant surface glycoprotein gene conversion in Trypanosoma rhodesiense.
We previously described a bloodstream Trypansoma rhodesiense clone, MVAT5-Rx2, whose isolation was based on its cross-reactivity with a monoclonal antibody (MAb) directed against a metacyclic variant surface glycoprotein (VSG). When the duplicated, expressed VSG gene in MVAT5-Rx2 was compared with its donor (basic copy) gene, 11 nucleotide differences were found in the respective 1.5-kb coding regions (Y. Lu, T. Hall, L. S. Gay, and J. E. Donelson, Cell 72:397-406, 1993). Here we describe a characterization of two additional bloodstream trypanosome clones, MVAT5-Rx1 and MVAT5-Rx3, whose VSGs are expressed from duplicated copies of the same donor VSG gene. The three trypanosome clones each react with the MVAT5-specific MAb, but they have different cross-reactivities with a panel of other MAbs, suggesting that their surface epitopes are similar but nonidentical. Each of the three gene duplication events occurs at a different 5' crossover site within a 76-bp repeat and is associated with a different set of point mutations. The 35, 11, and 28 point mutations in the duplicated VSG coding regions of Rx1, Rx2, and Rx3, respectively, exhibit a strand bias. In the sense strand, of the 74 total mutations generated in the three duplications, 54% are A-to-G or G-to-A (A:G) transitions and 7% are C:T transitions, while 26% are C:A transversions and 13% are C:G transversions. No T:G or T:A transversions occurred. Possible models for the generation of these point mutations are discussed.
Lu
Y
Y
Genetics Ph.D. Program, University of Iowa, Iowa City 52242.
Alarcon
C M
CM
Hall
T
T
Reddy
L V
LV
Donelson
J E
JE
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D001483:Base Sequence; D015139:Blotting, Southern; D003001:Cloning, Molecular; D003429:Cross Reactions; D003434:Crossing Over, Genetic; D017931:DNA Primers; D016054:DNA, Protozoan / Q000032:analysis / Q000235:genetics; D005455:Fluorescent Antibody Technique; D005785:Gene Conversion; D015870:Gene Expression; D008969:Molecular Sequence Data; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D012091:Repetitive Sequences, Nucleic Acid; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D016833:Trypanosoma brucei rhodesiense / Q000235:genetics*; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics*
D000911:Antibodies, Monoclonal; D017931:DNA Primers; D016054:DNA, Protozoan; D014643:Variant Surface Glycoproteins, Trypanosoma