Characterization of the Genetic Components of Streptomyces lividans Linear Plasmid SLP2 for Replication in Circular and Linear Modes

Abstract

ABSTRACT The nucleotide sequence of Streptomyces lividans linear plasmid SLP2 consists of 50,410 bp (C. H. Huang, C. Y. Chen, H. H. Tsai, C. Chen, Y. S. Lin, and C. W. Chen, Mol. Microbiol. 47: 1563-1576, 2003). Here we report that the basic SLP2 locus for plasmid replication in circular mode resembles that of Streptomyces linear plasmids pSLA2 and SCP1 and comprises iterons SLP2 and the adjacent rep SLP2 gene. More efficient replication additionally required the 47-bp sequence between bp 581 and 628 upstream of the iterons. Replacement of either the iterons or the rep gene of SLP2 by the corresponding genes of pSLA2 or SCP1 still allows propagation in Streptomyces , although the transformation frequencies were 3 orders of magnitude lower than the original plasmids, suggesting that these plasmids share similar replication mechanisms. To replicate SLP2 in linear mode, additional SLP2 loci—either mtap SLP2 / tpg SLP2 or mtap SLP2 / ilrA SLP2 —were required. IlrA SLP2 protein binds specifically to the iterons SLP2 in vitro. Interactions were detected between these SLP2-borne replication proteins (Mtap SLP2 , Tpg SLP2 , and IlrA SLP2 ) and the telomeric replication proteins (TpgL, TapL, and TpgL) of the S. lividans chromosome, respectively, but the SLP2 proteins failed to interact. These results suggest that SLP2 recruits chromosomally encoded replication proteins for its telomere replication.