Streptomyces Conjugative Genetic Elements
Jutta Vogelmann, Wolfgang Wohlleben and Günther Muth
from: Streptomyces: Molecular Biology and Biotechnology (Edited by: Paul Dyson). Caister Academic Press, U.K. (2011)
Antibiotic producing actinomycetes contain a huge variety of different plasmids, distinguished in size, topology, replication mechanism and copy number. Some are able to integrate into the chromosome by site specific recombination. With the exception of the huge linear plasmids, Streptomyces plasmids encode only functions involved in replication, stable maintenance and conjugative transfer. The Streptomyces conjugation system is unique, requiring a single plasmid-encoded protein, TraB. TraB is a hexameric ring ATPase with similarity to the septal DNA translocator proteins FtsK/SpoIIIE which are involved in chromosome segregation during cell division and sporulation. TraB binds non-covalently to 8bp TRS repeats present in the clt locus and transfers double stranded plasmid DNA from the donor to the recipient. Presence of clt-like sequences in the chromosome of S. coelicolor suggests that chromosomal genes are mobilized independently from the plasmid. Following primary transfer from the donor into the recipient, the plasmid is translocated via septal crosswalls resulting in intramycelial plasmid spreading. Plasmid spreading involves five to seven plasmid-encoded Spd-proteins. Protein-protein interaction studies with Spd-proteins of the conjugative plasmid pSVH1 suggest formation of a large DNA-translocation apparatus. One component, the integral membrane protein SpdB2 was shown to form pore structures in lipid bilayers read more ...