Characterization and Localization of Plasmid Functions Involved in Pock Formation and Pock Resistance of Plasmid pSK3*of Streptomyces kasugaensis MB273

SUMMARY: 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 (Porl 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.