Study on the specificity of DNA base sequence required for the transposition immunity of the (gamma) (delta) sequence

含有< γ >< δ >的质粒不能通过转座获得另一个< γ >< δ >的拷贝（转座免疫）。我们先前发现，< δ >末端的38-bp序列足以介导免疫。在目前的研究中。然而，< γ >-末端38bp的免疫活性较弱（1/45）。然后合成< γ >-末端38-bp序列，并克隆到质粒pUC13的smai位点，观察侧翼碱基序列对转座免疫效率的影响。将< γ >-末端38bp与天然侧翼序列之一GTAA克隆在一起。与人工smai位点序列TCCCC相比，免疫活性提高了7倍。这似乎表明转座免疫所需的碱基序列的特异性更倾向于富含at的侧翼序列而不是富含gt的侧翼序列。在第36 ~ 38位碱基序列中，ATG替代TAT使免疫降低1/28。由于ATG序列与AAG序列（< δ >-末端序列）仅相差一个碱基，而AAG具有最强的免疫力，因此对碱基37的特异性一定非常高。

A plasmid containing <gamma><delta> cannot acquire another copy of <gamma> <delta>by transposition (transposition immunity).We previously found that the 38-bp sequence of the <delta> terminal is sufficient to mediate the immunity. In the present study. however, the <gamma>-terminal 38 bp was shown to have weaker (1/45) immunity activity than the other. The <gamma>-terminal 38-bp sequence was then synthesized with and without a flanking 5-bp sequence and cloned into the SmaI-site of the plasmid pUC13 in order to see the effect of the flanking base sequence on the efficiency of transposition immunity. When the<gamma>-terminal 38 bp was cloned together with one of the natural flanking sequences GTAA. in stead of the artificial SmaI-site sequence TCCCC, immunity activity increased by 7-fold. It seems to suggest that the specificity of base sequence required for transposition immunity prefers AT-rich flanking sequence to GT-rich one. As for the base sequence between 36th and 38th, the substitution of TAT with ATG reduced the immunity by 1/28. Since the sequence ATG differs only one base from the sequnce AAG (the <delta>-terminal suquence), which had the strongest immunity, the specificity fo the base 37 must be extremely high.