AN UNUSUAL TYPE OF COINTEGRATE FORMATION BETWEEN A BACTEROIDES PLASMID AND THE EXCISED CIRCULAR FORM OF AN INTEGRATED ELEMENT (NBU1)

Evidence for an unusual type of cointegrate formation was found as the result of analyzing three integration events that fused a mobilizatio n-deficient Bacteroides plasmid (pEG920) with the excised circular for m of a nonreplicating Bacteroides element (NBU1). NBU1 is capable of i nserting itself into DNA segments, but the cointegrates were the resul t of invasion of NBU1 by pEG920, not vice versa. The same site on pEG9 20 was involved in all cases. Sequence analysis of the cointegrates su ggested that the integration events may have been the result of a mult istep process in which a conjugative transposon was involved. (C) 1994 Academic Press, Inc.