CHARACTERIZATION OF THE VARIABLE-NUMBER TANDEM REPEATS IN VRRA FROM DIFFERENT BACILLUS-ANTHRACIS ISOLATES

PCR analysis of 198 Bacillus anthracis isolates revealed a variable re gion of DNA sequence differing in length among the isolates. Five poly morphisms differed by the presence of two to six copies of the 12-bp t andem repeat 5'-CAATATCAACAA-3'. This variable-number tandem repeat (V NTR) region is located within a larger sequence containing one complet e open reading frame that encodes a putative 30-kDa protein, Length va riation did not change the reading frame of the encoded protein and on ly changed the copy number of a 4-amino-acid sequence (QYQQ) from 2 to 6, The structure of the VNTR region suggests that these multiple repe ats are generated by recombination or polymerase slippage, Protein str uctures predicted from the reverse-translated DNA sequence suggest tha t any structural changes in the encoded protein are confined to the re gion encoded by the VNTR sequence, Copy number differences in the VNTR region were used to define five different B. anthracis alleles, Chara cterization of 198 isolates revealed allele frequencies of 6.1, 17.7, 59.6, 5.6, and 11.1% sequentially from shorter to longer alleles, The high degree of polymorphism in the VNTR region provides a criterion fo r assigning isolates to five allelic categories, There is a correlatio n between categories and geographic distribution, Such molecular marke rs can be used to monitor the epidemiology of anthrax outbreaks in dom estic and native herbivore populations.