Hughes J E, Welker D L
Department of Biology, Utah State University, Logan 84322-5500.
Plasmid. 1989 Nov;22(3):215-23. doi: 10.1016/0147-619x(89)90004-8.
Copy number of the endogenous nuclear plasmids of Dictyostelium discoideum is a plasmid-specific trait. Copy number is stable over time, is constant relative to ploidy level, is independent of host cell genetic background, and is independent of the presence of a second unrelated plasmid in the same nucleus. Unrelated plasmids are compatible with one another within a single nucleus. Pairwise combinations of Ddp1, Ddp2, and Ddp5 were stably maintained over many generations in the absence of selection. In contrast, one of the D. discoideum plasmids (Ddp2) was incompatible with a recombinant plasmid derived from it (p7d2). In the absence of selection for retention of p7d2, transformants contain either one or the other but not both plasmids. The plasmids are stably maintained in host cells with differing genetic backgrounds, although plasmid-free colonies were detected at a frequency of about 1-2% in populations of some strains after 50 generations growth following a previous cloning.
盘基网柄菌内源性核质粒的拷贝数是质粒特异性的特征。拷贝数随时间稳定，相对于倍性水平恒定，独立于宿主细胞遗传背景，且独立于同一细胞核中第二个不相关质粒的存在。不相关的质粒在单个细胞核内彼此兼容。在没有选择压力的情况下，Ddp1、Ddp2和Ddp5的两两组合在许多代中都能稳定维持。相比之下，盘基网柄菌的一种质粒（Ddp2）与源自它的重组质粒（p7d2）不兼容。在没有选择保留p7d2的情况下，转化体要么含有其中一种质粒，要么含有另一种质粒，但不会同时含有两种质粒。这些质粒在具有不同遗传背景的宿主细胞中能稳定维持，尽管在先前克隆后经过50代生长的某些菌株群体中，以约1 - 2%的频率检测到无质粒菌落。
