THE TERMINAL STRUCTURES OF LINEAR PLASMIDS FROM RHODOCOCCUS-OPACUS

The telomers of several linear plasmids of Rhodococcus opacus (formerl y Nocardia opaca) were studied. The plasmids pHG201, pHGZ04 and pHG205 carry proteins bound to their ends, as shown by gel retardation exper iments. A sequence hybridizing with the terminal sequence of pHG207, a recombinant linear plasmid consisting of the left part of pHG204 and the right part of pHG205, which was analysed in a previous study by th e authors could be detected in all linear plasmids of the wild-type R. opacus strains MR11 and MR22. However, only pHG204 and pHG206 carry t erminal inverted repeats (TIRs) like pHG207. Cloning and sequencing of the terminal fragment of pHG204 revealed a nearly perfect TIR of 1016 bp. In contrast, the termini of pHG201 and pHG205 share little homolo gy. Sequence analysis of the two end fragments of pHG201 revealed a si milarity of only 65% within the terminal 34/32 bp and a perfect TIR of only 3 bp. The results support the assumption that long TIRs are not absolutely necessary for replication and maintenance of linear plasmid s.