Chaconas G, Gloor G, Miller J L
J Biol Chem. 1985 Mar 10;260(5):2662-9.
The A and B proteins encoded by the temperate bacteriophage Mu are involved in the high efficiency DNA transposition reaction which is the distinguishing feature of this phage. The genes encoding these early proteins were cloned in an expression vector under the control of the bacteriophage lambda leftward promoter. Under optimal conditions gpB was overproduced to account for 15% of the total cellular protein. The protein was purified to near homogeneity as determined by silver staining. Sequence analysis of the N terminus confirmed the identity of the purified protein as gpB. Proteolytic processing of the B protein does not occur at the amino terminus; the terminal methionine residue is quantitatively deformylated. The protein, which was found to be basic and a general DNA binding protein, was insoluble at low ionic strength in the absence, but not in the presence, of DNA. The B protein also displayed a tendency to aggregate at high ionic strength where it was soluble in the absence of DNA. In addition, the protein was characterized as to its amino acid composition and extinction coefficient at 280 nm. The purified protein is active in a soluble in vitro transposition-replication system.
温和噬菌体Mu编码的A和B蛋白参与了高效DNA转座反应，这是该噬菌体的显著特征。编码这些早期蛋白的基因被克隆到一个受噬菌体λ左向启动子控制的表达载体中。在最佳条件下，gpB过量表达，占细胞总蛋白的15%。通过银染确定，该蛋白被纯化至接近均一。N端的序列分析证实纯化的蛋白为gpB。B蛋白在氨基端不发生蛋白水解加工；末端甲硫氨酸残基被定量去甲酰化。该蛋白被发现呈碱性且是一种通用的DNA结合蛋白，在无DNA时于低离子强度下不溶，但在有DNA时可溶。B蛋白在高离子强度下也有聚集倾向，在无DNA时可溶。此外，还对该蛋白的氨基酸组成和280nm处的消光系数进行了表征。纯化的蛋白在一个可溶性体外转座-复制系统中具有活性。
