Chase J W, Rabin B A, Murphy J B, Stone K L, Williams K R
J Biol Chem. 1986 Nov 15;261(32):14929-35.
We have determined the sequence of the gene encoding the large subunit of Escherichia coli exonuclease VII (xseA) and the amino acid sequence of the protein it encodes. The coding region of the xseA gene is 1368 base pairs. The protein encoded by the gene contains 456 amino acids and has a calculated molecular weight of 51,823. The promoter for xseA is close to that for guaB, and these two genes are transcribed in opposite directions: xseA clockwise and guaB counterclockwise on the standard E. coli genetic map. The cloned xseA gene can complement an xseA deletion mutant strain. In an xseA+ genetic background production of large quantities of the xseA gene product appeared to decrease the amount of exonuclease VII activity in cell extracts. In fact, no exonuclease VII activity at all could be detected following induction of strains in which the xseA gene was under lambda pL regulation. These observations suggest that the proper ratio of the large and small exonuclease VII subunits must be maintained in order to produce active enzyme.
我们已经确定了编码大肠杆菌核酸外切酶VII大亚基（xseA）的基因序列及其编码蛋白质的氨基酸序列。xseA基因的编码区为1368个碱基对。该基因编码的蛋白质含有456个氨基酸，计算分子量为51,823。xseA的启动子靠近guaB的启动子，这两个基因转录方向相反：在标准大肠杆菌遗传图谱上，xseA顺时针转录，guaB逆时针转录。克隆的xseA基因可以互补xseA缺失突变株。在xseA+遗传背景下，大量产生xseA基因产物似乎会降低细胞提取物中核酸外切酶VII的活性。事实上，在受λ pL调控的xseA基因诱导菌株中，完全检测不到核酸外切酶VII的活性。这些观察结果表明，为了产生有活性的酶，必须维持核酸外切酶VII大小亚基的适当比例。
