Aleksenko A, Nikolaev I, Vinetski Y, Clutterbuck A J
Division of Molecular Genetics, University of Glasgow, UK.
Mol Gen Genet. 1996 Nov 27;253(1-2):242-6. doi: 10.1007/s004380050318.
Plasmids bearing the AMA1 replicator from Aspergillus nidulans are capable of extrachromosomal replication in this fungus as well as in other species. Synthetic plasmids bearing the moderately expressed argB gene and the highly expressed, inducible beta-galactosidase gene (bgaS) were introduced into fungal cells. Expression of both genes was monitored by Northern hybridization. It was demonstrated that transcription of bgaS is induced and repressed normally, irrespective of whether the gene is integrated into the chromosome or maintained on an extrachromosomal supercoiled plasmid. Transcription of the strongly expressed bgaS gene stimulates transcription of the argB gene located on the same replicating plasmid irrespective of orientation. This effect also occurs with chromosomally integrated vectors, but to a lesser extent. Episomal vectors are present in 10 copies per nucleus, and the expression level of the argB gene is approximately proportional to copy number. However, the amount of mRNA transcribed from the highly expressed bgaS gene on the multi-copy replicating plasmid does not exceed that from single-copy integrants. High levels of expression of the plasmid-borne gene do not affect plasmid mitotic stability or copy number.
携带构巢曲霉AMA1复制子的质粒能够在这种真菌以及其他物种中进行染色体外复制。将携带中度表达的argB基因和高度表达的、可诱导的β-半乳糖苷酶基因（bgaS）的合成质粒导入真菌细胞。通过Northern杂交监测这两个基因的表达。结果表明，无论该基因是整合到染色体上还是维持在染色体外超螺旋质粒上，bgaS的转录都能正常诱导和抑制。强表达的bgaS基因的转录会刺激位于同一复制质粒上的argB基因的转录，而与方向无关。这种效应在染色体整合载体中也会出现，但程度较小。游离型载体每个细胞核中有10个拷贝，argB基因的表达水平与拷贝数大致成正比。然而，多拷贝复制质粒上高表达的bgaS基因转录的mRNA量不超过单拷贝整合体的转录量。质粒携带基因的高水平表达不会影响质粒的有丝分裂稳定性或拷贝数。
