Characterization and localization of plasmid functions involved in pock formation and pock resistance of plasmid pSK3 of Streptomyces kasugaensis MB273.

Deletion derivatives and recombinants of the plasmid pSK3, which is a cointegrate of pSK1 and pSK2 in Streptomyces kasugaensis, were constructed and analysed for their ability to transfer and 'pock' on strains carrying pSK1 or pSK2. Various deletions in the pSK1 and/or pSK2 regions of pSK3 were grouped into nine classes on the basis of their pock-forming ability and pock resistance. Analysis of these deletions and insertions provided tentative locations of DNA regions for two pock-resistance determinants (Por1 and Por2), two pock-forming determinants (Poc1 and Poc2) consisting of plasmid transfer and spread determinants (Tra/Spr), and two replication determinants (Rep1 and Rep2) corresponding to the pSK1 and pSK2 regions of pSK3. In particular, the Por2 function in the pSK2 region was determined to be located in a 1.35 kb segment.