Wirtz U, Osborne B, Baker B
Department of Plant Pathology, University of California, Berkeley 94720, USA.
Plant J. 1997 Jan;11(1):125-35. doi: 10.1046/j.1365-313x.1997.11010125.x.
Analysis of transposition products generated after Activator (Ac) excision from the P locus in maize suggest that Ac excises either during or after replication of the P locus. The frequency of excision of the non-autonomous Ac derivative, Dissociation (Ds), from extrachromosomal replicating and nonreplicating vector DNAs in transfected black mexican sweet maize protoplasts was compared to assess directly a role of extrachromosomal vector DNA replication in Ds excision. Replicating (rep+) and nonreplicating (rep-) vector DNAs comprised a Ds element that harbored a geminivirus, wheat dwarf virus (WDV), origin of replication and WDV genes required for viral DNA replication (rep+) or mutant, inactive derivatives of these genes (rep-). Excision of Ds was detected only in those cell nuclei co-transfected with the replicating Ds-vector DNA and a transposase expression vector. Quantitative reconstruction experiments showed that Ds excised at least 3 x 10(5)-fold more frequently from replicating vector DNA as compared with nonreplicating vector DNA. Therefore, these results provide direct evidence for a coupling of Ds excision from extrachromosomal vector DNA to vector DNA replication in maize.
对玉米P位点上激活子（Ac）切除后产生的转座产物进行分析表明，Ac在P位点复制期间或之后切除。比较了转染的黑色墨西哥甜玉米原生质体中，非自主Ac衍生物解离因子（Ds）从染色体外复制和非复制载体DNA上切除的频率，以直接评估染色体外载体DNA复制在Ds切除中的作用。复制型（rep +）和非复制型（rep-）载体DNA包含一个Ds元件，该元件带有双生病毒小麦矮缩病毒（WDV）的复制起点以及病毒DNA复制所需的WDV基因（rep +）或这些基因的突变失活衍生物（rep-）。仅在与复制型Ds载体DNA和转座酶表达载体共转染的细胞核中检测到Ds的切除。定量重建实验表明，与非复制型载体DNA相比，Ds从复制型载体DNA上切除的频率至少高3×10^5倍。因此，这些结果为玉米中Ds从染色体外载体DNA上的切除与载体DNA复制的偶联提供了直接证据。
