Mycobacterial linear plasmids have an invertron-like structure related to other linear replicons in actinomycetes

The authors previously identified large plasmids in Mycobacterium xenopi, M. branderi and M. celatum which appeared to have a linear topology. This study has confirmed the presence of such linear plasmids in mycobacteria, including M. avium, and demonstrated that the ends of these replicons are covalently bound with protein(s), suggesting an invertron-like structure. The termini of one 25 kb plasmid, designated pCLP, from M. celatum were cloned and the first 500 bp of each terminus were sequenced. The termini of this plasmid show the characteristic features of invertrons with terminal inverted repeats of 45 bp (with imperfect matches) and several palindromic sequences. Moreover, similarity existed in the structure and terminal nucleotide sequence of pCLP and the termini of linear replicons of Streptomyces and Rhodococcus species, indicating a conservation of these linear extrachromosomal elements within the Actinomycetales.