Pazour G J, Das A
Department of Biochemistry, University of Minnesota, St Paul 55108.
Nucleic Acids Res. 1990 Dec 11;18(23):6909-13. doi: 10.1093/nar/18.23.6909.
Expression of Agrobacterium tumefaciens virulence (vir) genes is dependent on the presence of a conserved 'vir box' sequence in their 5' nontranscribed regions. The location and number of these sequences vary considerably in different vir genes. Site-directed mutagenesis was used to identify the functional vir box(es) of virB, virC and virD. For virB expression both vir box B1 and B2 are required but only the vir box B1 is absolutely essential. Of the five vir boxes of virC and virD two are required for virC expression while only one vir box is required for virD expression. To investigate the minimum sequences necessary for vir gene induction a deletion derivative of virE that lacks the vir box region was used. This mutant is not induced by acetosyringone. The inducibility of this promoter was restored when a synthetic deoxyoligonucleotide dGTTTCAATTGAAAC was introduced at a location analogous to that of the wild type vir box sequence. Mutational analysis indicate that the functional vir box sequence is 14 residues in length, contains a dyad symmetry and has the consensus sequence d ryTncAaTTGnAaY [corrected] (r = purine, y = pyrimidine).
根癌农杆菌毒性（vir）基因的表达取决于其5'非转录区中保守的“vir框”序列的存在。这些序列的位置和数量在不同的vir基因中差异很大。采用定点诱变来鉴定virB、virC和virD的功能性vir框。对于virB的表达，vir框B1和B2都是必需的，但只有vir框B1是绝对必需的。在virC和virD的五个vir框中，两个是virC表达所必需的，而virD表达只需要一个vir框。为了研究vir基因诱导所需的最小序列，使用了缺失vir框区域的virE缺失衍生物。该突变体不会被乙酰丁香酮诱导。当在与野生型vir框序列类似的位置引入合成脱氧寡核苷酸dGTTTCAATTGAAAC时，该启动子的诱导性得以恢复。突变分析表明，功能性vir框序列长度为14个残基，包含一个二元对称，共有序列为d ryTncAaTTGnAaY [已校正]（r = 嘌呤，y = 嘧啶）。
