ten Lohuis M, Müller A, Heidmann I, Niedenhof I, Meyer P
Max Delbrueck-Laboratorium in der MPG, Köln, Germany.
Plant J. 1995 Dec;8(6):919-32. doi: 10.1046/j.1365-313x.1995.8060919.x.
A 1.6 kb repetitive DNA sequence (RPS) from Petunia hybrida was identified that destabilizes expression of a GUS marker transgene. Following polyethylene glycol (PEG)-mediated tobacco and petunia protoplast transformations, GUS expression patterns analysed on callus and plant levels were clearly more variable when constructs contained the RPS sequence. The effect on transgene expression required chromosomal integration since the two different RPS constructs employed did not exhibit reduced levels of GUS activities in transient assays. DNA methylation analysis implies a hypermethylated default state of endogenous RPS copies present in the petunia genome. Analysis of the transgene DNA in different transgenic tobacco plants showed almost complete hypermethylation of a particular Hhal site of the RPS sequence. It is proposed that, due to the presence of specific signals within the RPS region or based on interaction of RPS with other endogenous homologous sequences, RPS functions as an initiation region for de novo methylation and induces expression variegation in adjacent sequences.
从矮牵牛中鉴定出一个1.6 kb的重复DNA序列（RPS），它会使GUS标记转基因的表达不稳定。在聚乙二醇（PEG）介导的烟草和矮牵牛原生质体转化后，当构建体包含RPS序列时，在愈伤组织和植株水平上分析的GUS表达模式明显更具变异性。对转基因表达的影响需要染色体整合，因为所使用的两种不同RPS构建体在瞬时分析中未表现出GUS活性水平降低。DNA甲基化分析表明矮牵牛基因组中存在的内源性RPS拷贝处于高甲基化默认状态。对不同转基因烟草植株中转基因DNA的分析显示，RPS序列的一个特定Hhal位点几乎完全高甲基化。有人提出，由于RPS区域内存在特定信号或基于RPS与其他内源性同源序列的相互作用，RPS作为从头甲基化的起始区域，并诱导相邻序列中的表达斑驳。
