Odd number of crossover events between two circular DNA molecules would form a co-integrated circular DNA molecule,while it occurs in two linear DNA molecules that would generate two recombinant DNA fragments with arm exchanged [1.2.5].Gram-positive.mycelia,and differentiating Streplomyces carries linear chromosomes and linear plasmids with terminal proteins covalently bound to the 5 ends of the DNA.In previous study,we transferred a linear plasmid [4]carrying a 32 kb DNA fragment of SCP1 plasmid into a Streptomyces strain with SCP1 plasmid.