SEQUENCE AND FUNCTIONAL-ANALYSIS OF THE STREPTOMYCES PHAEOCHROMOGENESPLASMID PJV1 REVEALS A MODULAR ORGANIZATION OF STREPTOMYCES PLASMIDS THAT REPLICATE BY ROLLING CIRCLE

pJV1 is an 11 kb, high-copy-number conjugative Streptomyces phaeochrom ogenes plasmid that replicates by the rolling circle mechanism (RCR). Sequencing combined with functional analysis of deletion, insertion an d 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) determin ant. pJV1 contains two essential transfer genes whose expression is re gulated by an adjacent repressor gene with similarity to the GntR fami ly of regulators. A consensus sequence specific for the helix-turn-hel ix motifs of repressor proteins of Streptomyces plasmids is proposed. Unregulated expression of the transfer genes by inactivation of the re pressor is lethal. Three additional genes increase intramycelial plasm id spread resulting in pock formation but unlike the essential transfe r genes, are not required for Cma. The pJV1 transfer genes and their r egulatory region, but not the minimal replication region encoding the double-strand replication origin and replication protein, are similar in sequence and arragement to those of the Streptomyces nigrifaciens p lasmid pSN22, revealing a modular organization of Streptom PCR plasmid s.