λ噬菌体nutL序列突变对N蛋白生物功能的影响

The Effect of nutL Mutation on Lambda Phage N\|mediated Gene Regulation

λ噬菌体 Ｎ 蛋白不仅是抗转录终止的正调控因子，也是在翻译水平上阻遏自身基因表达的负调控蛋白．ｎｕｔ Ｒ Ｎ Ａ 位点（包括 ｂｏｘ Ａ 和 ｂｏｘ Ｂ）参与了这两种生物效应．对位于左向操纵子（ｐ Ｌ）的 ｎｕｔ Ｌ 序列进行了突变后，证明 ｎｕｔ Ｌ 缺失及 ｂｏｘ Ｂ 第 ６ 位核苷酸突变使 Ｎ 丧失了正、负调控功能，提示 ｎｕｔ Ｌ 在 Ｎ 介导的调控反应中是必需的．ｎｕｔ Ｌ 序列中 ｂｏｘ Ａ 单碱基突变使 Ｎ 丧失了正调控功能，部分保留了负调控功能．这种负调控作用导至极性效应，使 ｌａｃ Ｚ基因转录水平明显下降．

Lambda Phage N protein regulates the transcription of early phage genes by participating in the formation of a terminator resistant transcription complex and therefore positively regulates the expression of genes lying downstrean of transcriptional terminators.N also has an additional regulatory role,as a repressor of translation of its own gene.Using a lacZ and galK double reporter system,β galactosidase and galactokinase levels reflected the degree of N\|mediated translation repression of an N lacZ gene fusion and transcription antitermination through terminators to galK .The relationship between the two N\|mediated functions was explored. nutL was the RNA site to which N bound to carry out these functions.As expected a nutL deletion and a single base substitution in the N binding site of nutL ( boxB) eliminated both N mediated functions.Another part of nutL (boxA ) was also tested.It is thought to bind Nus factors required for antitermination with N. box A mutations eliminated antitermination instead of translation repression by N protein.