McCommas S A, Syvanen M
Department of Biological Sciences, Southern Illinois University, Edwardsville 62026.
J Bacteriol. 1988 Feb;170(2):889-94. doi: 10.1128/jb.170.2.889-894.1988.
IS50R is an insertion sequence associated with the transposon Tn5. IS50R carries the structural genes for two proteins; one (P1) is the Tn5 transposase, and the other (P2) is an inhibitor of transposition. These two proteins are translated from two different transcripts, m1 and m2. When bacteriophage lambda::IS50R DNA was introduced into a bacterial cell, m1 and m2 were initially at relative levels of about 1 to 2. As time progressed the amount of m1 fell, whereas the amount of m2 continued to increase, until after about 3 h the ratio of m1 to m2 was about 1 to 80. The temporal changes in the levels of these transcripts correlated with temporal changes in P1 and P2 levels and Tn5 transposition that have been documented in other studies. We measured the stability of the messages and showed that the differences in the levels of m1 and m2 must reflect real differences in the strengths of their promoters and that the changes in transcription kinetics are mediated by the dam methylation system of the cell and are not determined by IS50R products. Our results show that the 5' end of m2 is about twice as stable as that of m1, which raises the possibility that differential message stability does, in part, influence the ratio of inhibitor to transposase.
IS50R是一种与转座子Tn5相关的插入序列。IS50R携带两种蛋白质的结构基因；一种（P1）是Tn5转座酶，另一种（P2）是转座抑制剂。这两种蛋白质由两种不同的转录本m1和m2翻译而来。当噬菌体λ::IS50R DNA被导入细菌细胞时，m1和m2最初的相对水平约为1比2。随着时间的推移，m1的量下降，而m2的量持续增加，直到大约3小时后，m1与m2的比例约为1比80。这些转录本水平的时间变化与其他研究中记录的P1和P2水平以及Tn5转座的时间变化相关。我们测量了这些信息的稳定性，并表明m1和m2水平的差异必定反映了它们启动子强度的实际差异，并且转录动力学的变化是由细胞的dam甲基化系统介导的，而不是由IS50R产物决定的。我们的结果表明，m2的5'端稳定性约为m1的两倍，这增加了差异信息稳定性在一定程度上影响抑制剂与转座酶比例的可能性。
