Cohen A, Bar-Nir D, Goedeke M E, Parag Y
Plasmid. 1985 Jan;13(1):41-50. doi: 10.1016/0147-619x(85)90054-x.
A 16.6-kb plasmid-pSG1-was isolated from Streptomyces griseus following transformation of protoplasts with unrelated plasmids. Southern hybridization experiments with radioactive probes prepared from pSG1 fragments and immobilized S. griseus DNA fragments indicated that the plasmid was present in the progenitor strain, in an integrated state. In the pSG1+ isolates plasmid sequences existed both as integrated sequences and as free plasmids. The integrated state of maintenance persisted in strains which have been cured of the free plasmid. The junction site on the plasmid was located on a 0.5-kb EcoRI-SalI fragment. The chromosomal integration site was demonstrated to be the same in all strains derived from S. griseus NRRL3851. The occurrence of both states of plasmid maintenance in the same clones indicates that an integrated pSG1 sequence does not interfere with free plasmid replication and partition. It suggests that the establishment of the free state may involve a replicative excision of pSG1 from the S. griseus chromosome.
用不相关的质粒对灰色链霉菌原生质体进行转化后，从该菌中分离出了一个16.6kb的质粒-pSG1。用从pSG1片段制备的放射性探针和固定的灰色链霉菌DNA片段进行的Southern杂交实验表明，该质粒以整合状态存在于祖代菌株中。在pSG1+分离株中，质粒序列既以整合序列形式存在，也以游离质粒形式存在。在已消除游离质粒的菌株中，维持整合状态依然存在。质粒上的连接位点位于一个0.5kb的EcoRI-SalI片段上。已证明，在所有源自灰色链霉菌NRRL3851的菌株中，染色体整合位点是相同的。同一克隆中质粒维持的两种状态的出现表明，整合的pSG1序列不会干扰游离质粒的复制和分配。这表明游离状态的建立可能涉及pSG1从灰色链霉菌染色体上的复制性切除。
