Servín-González L, Sampieri A I, Cabello J, Galván L, Juárez V, Castro C
Departamento de Biología Molecular, Universidad Nacional Autónoma de México, Cd. Universitaria, DF, Mexico.
Microbiology (Reading). 1995 Oct;141 ( Pt 10):2499-510. doi: 10.1099/13500872-141-10-2499.
pJV1 is an 11 kb, high-copy-number conjugative Streptomyces phaeochromogenes plasmid that replicates by the rolling circle mechanism (RCR). Sequencing combined with functional analysis of deletion, insertion and frameshift mutations was used to characterize the genes involved in plasmid transfer and chromosome mobilization (Cma), the single-strand origin for RCR and an associated strong incompatibility (Sti) determinant. pJV1 contains two essential transfer genes whose expression is regulated by an adjacent repressor gene with similarity to the GntR family of regulators. A consensus sequence specific for the helix-turn-helix motifs of repressor proteins of Streptomyces plasmids is proposed. Unregulated expression of the transfer genes by inactivation of the repressor is lethal. Three additional genes increase intramycelial plasmid spread resulting in pock formation but, unlike the essential transfer genes, are not required for Cma. The pJV1 transfer genes and their regulatory region, but not the minimal replication region encoding the double-strand replication origin and replication protein, are similar in their sequence and arrangement to those of the Streptomyces nigrifaciens plasmid pSN22, revealing a modular organization of Streptomyces RCR plasmids.
pJV1是一个11 kb的高拷贝数接合型嗜铬链霉菌质粒，通过滚环机制（RCR）进行复制。结合缺失、插入和移码突变的功能分析进行测序，以表征参与质粒转移和染色体动员（Cma）、RCR的单链起始位点以及相关强不相容性（Sti）决定簇的基因。pJV1包含两个必需的转移基因，其表达受一个与GntR家族调节因子相似的相邻阻遏基因调控。提出了链霉菌质粒阻遏蛋白螺旋-转角-螺旋基序特有的共有序列。通过使阻遏基因失活来无调控地表达转移基因是致死性的。另外三个基因增加了菌丝内质粒的传播，导致痘疱形成，但与必需的转移基因不同，它们不是Cma所必需的。pJV1转移基因及其调控区域，而非编码双链复制起点和复制蛋白的最小复制区域，在序列和排列上与黑化链霉菌质粒pSN22相似，揭示了链霉菌RCR质粒的模块化组织。
