Lagos R, Goldstein R
Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
Arch Biol Med Exp. 1987;20(3-4):325-32.
Phasmid (phage-plasmid) P4 is capable of propagating as a temperate phage, lytic helper-dependent phage, and as a plasmid (pP4vir1). Alteration of cellular growth conditions can be used to manipulate the copy number (n) of pP4vir1 from low (n = 1-2) to high (n = 30-40). The levels of gene expression of P4 in the plasmid and phage states are radically different. While there is high expression of P4 proteins in the phage state, low levels of gene expression are found in the plasmid mode of propagation thereby allowing pP4vir1 to remain intracellularly without perturbing host homeostasis. Possible evolutionary origins of phasmid P4 are discussed.
噬菌粒（噬菌体 - 质粒）P4能够作为温和噬菌体、裂解性辅助依赖噬菌体以及质粒（pP4vir1）进行增殖。改变细胞生长条件可用于将pP4vir1的拷贝数（n）从低水平（n = 1 - 2）调控到高水平（n = 30 - 40）。P4在质粒状态和噬菌体状态下的基因表达水平截然不同。在噬菌体状态下P4蛋白有高表达，而在质粒增殖模式下基因表达水平较低，从而使pP4vir1能够留在细胞内而不干扰宿主的稳态。文中还讨论了噬菌粒P4可能的进化起源。
