Tandem repetition of the 5' mini-exon of variant surface glycoprotein genes: a multiple promoter for VSG gene transcription?
Activation of some variant surface glycoprotein (VSG) genes involves a duplicative transposition to an expression site, which completes the gene by addition of a mini-exon coding for the 5' 35 nucleotides of VSG mRNAs. Using a 22 nucleotide probe we have found some 200 copies of the mini-exon on a tandemly arranged 1.35 kb repetitive element. This repeat is highly conserved in three trypanosome species. The mini-exon on the repeat is flanked by a 5' splice site that resembles the consensus sequence. We have not found a single mini-exon within 10 kb of the transposed VSG gene exon in the expression site. We propose a model in which the arrays of mini-exon repeats function as a repetitive promoter for efficient transcription of VSG genes.
D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D004262:DNA Restriction Enzymes / Q000378:metabolism; D015252:Deoxyribonucleases, Type II Site-Specific; D006023:Glycoproteins / Q000235:genetics*; D009693:Nucleic Acid Hybridization; D012091:Repetitive Sequences, Nucleic Acid; D014158:Transcription, Genetic; D014346:Trypanosoma brucei brucei / Q000235:genetics*; D014643:Variant Surface Glycoproteins, Trypanosoma
D006023:Glycoproteins; D014643:Variant Surface Glycoproteins, Trypanosoma; D004262:DNA Restriction Enzymes; C028649:endodeoxyribonuclease XmnI; D015252:Deoxyribonucleases, Type II Site-Specific; C040158:GTAC-specific type II deoxyribonucleases