Jt. Pembroke et Db. Murphy, Isolation and analysis of a circular form of the IncJ conjugative transposon-like elements, R391 and R997: implications for IncJ incompatibility, FEMS MICROB, 187(2), 2000, pp. 133-138
The incompatibility between the chromosomally integrating, conjugative tran
sposon-like, IncJ elements R997 (ampicillin resistant) and R391 (kanamycin
resistant) was examined by constructing strains harbouring both elements. U
nusually, recA(+) strains harbouring the resistance determinants of both el
ements could be isolated but all strains lacked detectable extrachromosomal
DNA. The phenotypic characteristics and transfer patterns observed suggest
ed the formation;of recombinant hybrids lather than strains harbouring both
elements independently. formation of strains harbouring two IncJ elements
in a recA background was thus examined and resulted in the visualisation of
extrachromosomal DNA. When R391 was transferred to a recA strain containin
g integrated R997, both elements co-existed stably and resulted in the isol
ation of a plasmid of 93.9 kb. When R997 was transferred to a recA strain h
arbouring an integrated R391, a plasmid of 85 kb was isolated. Comparison o
f restriction patterns For both elements revealed many common and several d
istinct fragments indicating a close physical relationship. These data sugg
est that although IncJ elements normally integrate at a unique site in the
Escherichia coil chromosome, they possess the ability for autonomous replic
ation which becomes manifest in a recA background when this site is occupie
d. This observation has implications For the nature of the incompatibility
associated with IncJ elements and also provides a reliable method for isola
ting IncJ elements for molecular characterisation. (C) 2000 Federation of E
uropean Microbiological Societies. Published by Elsevier Science B.V, All r
ights reserved.