In addition , no back mutation to obtain a maximal complexity ( i . e . - resistant and sensitive species coexistence ) or original ecology ( i . e . original - lysogen ) for the evolution occurs 而且，逆反应变异回原有菌相而成对噬菌体敏感及阻抗菌相共存之最大分歧度或回归至起始单一对噬茵体敏感菌相并未曾演化发生。
2.
Addition of iptg to growing culture of the lysogen induces t7 rna polymerase , which in turn transcribe the target dna in the plasmid . in the presence of glucose and appropriate conditions such as temperature and concerntration of iptg , a 52kd protein with tryptopanase activity was expressed 摸索发酵条件，如改变培养温度和iptg浓度等，发现在30培养条件下， 0 . 2mmiptg诱导时，发酵液中的吲哚含量最高，表明低浓度的诱导剂或低温诱导有利于表达出有活性的色氨酸酶。
3.
To prove that the cloned dna fragment can express tryptopanase , a new plasmid pet28c - tnaa , in which the cloned dna fragment was located downstream of t7 promoter on pet28c was constructed and transformed into host bl21 ( de3 ) , a bl21 lysogen of bacteriophage de3 in which the only promoter known to direct transcription of the t7 rna polymerase gene is the lacuvs promoter , which is inducible by iptg 用iptg诱导表达t7rna聚合酶，以表达质粒上的目的基因。在葡萄糖存在的条件下，用常规方法发酵和诱导( 37 1mmiptg ) ，发现表达的蛋白质条带的分子量与理论上计算的分子量一致。但是发酵液中检测不到吲哚，表明虽然表达了目标蛋白，但表达的蛋白质没有酶活性。
