IN-VIVO ANALYSIS OF THE PLASMID PAM-BETA-1 RESOLUTION SYSTEM

The promiscuous plasmid pAM beta 1 from Gram-positive bacteria encodes a resolution system which differs from that of Tn3 in that (i) it req uires a histone-like protein and an unusual resolvase-DNA interaction to promote recombination and (ii) it mediates in vivo DNA inversion in plasmid substrates. In this in vivo analysis, the pAM beta 1 resoluti on site is narrowed down to a 99 bp segment, the strand exchange is ma pped within 10 bp and the serine residue at position 10 of the resolva se is shown to be essential for enzyme activity. In addition, data sho wing that the resolution system does not promote DNA inversion in the Bacillus subtilis chromosome are presented. Implications of this obser vation are discussed.