The unstable region of Streptomyces ambofaciens includes 210 kb terminal inverted repeats flanking the extremities of the linear chromosomal DNA

Abstract

Physical maps of the chromosomes of three strains of Streptomyces ambofaciens were constructed by ordering Asel fragments generated from the genomic DNA as a single linear chromosome of about 8 Mb. The physical maps of the three strains were very similar. For strain DSM40697, a Dral map was obtained by positioning the Dral sites relative to the Asel map. Eighteen genetic markers as well as the deletable and amplifiable region were assigned to the Asel and Dral fragments in this strain. The resulting genetic map resembled that of Streptomyces coelicolor A3(2). The two terminal Asel fragments exhibited retarded pulsed-field gel electrophoresis mobility, demonstrating that proteins are covalently bound at this position. A restriction map of this region was made using four additional endonucleases. Repeated sequences present at both ends of the chromosome were mapped as long terminal inverted repeats stretching over 210 kb. This corresponds to the longest terminal inverted repeats so far characterized. The deletable region of S. ambofaciens was localized at the chromosomal extremities.

Chromosomal Circularization inStreptomyces griseusby Nonhomologous Recombination of Deletion Ends

“…Chromosomal circularization was also indicated in S. lividans 1,13) and S. ambofaciens 4) by detection of a fused macrorestriction fragment. In addition, Qin and Cohen 15) reported the circularization of artiˆcial pSLA2 plasmids in S. lividans by nonhomologous recombination of deletion ends.…”

“…Filamentous soil bacteria, Streptomyces, are unusual in carrying an 8-9 Mb linear chromosome: [1][2][3][4][5][6][7] the genome project for Streptomyces coelicolor A3(2), a model strain for Streptomyces genetics, has been recently completed. 8) Streptomyces species are also known to frequently have linear plasmids, which range from 12 to 1700 kb in size.…”

“…Chromosomal circularization in Streptomyces waŝ rst indicated by detection of a macrorestriction fusion fragment in deletion mutants of Streptomyces lividans 1,13) and Streptomyces ambofaciens. 4) It waŝ nally conˆrmed in Streptomyces griseus by cloning and sequencing of the fusion junctions of the circularized chromosomes. 14) No homology and a 6-bp microhomology were detected between the right and left deletion ends of the mutant chromosomes.…”

Dynamic bacterial genome organization

“…Examples are Bacillus subtilis 29, adenovirus, transposable elements in maize, and P-elements from Drosophila cells (Sakaguchi, 1990). Invertrons may also constitute the ends of a linear chromosome, as seen in the genus Streptomyces (Leblond et al, 1996;Hinnebusch and Tilly, 1993); in some strains of Streptomyces ambofaciens, the inverted repeats flanking the extremities of the linear 8 Mb chromosomal DNA are more than 200 kb. (Leblond et al, 1996).…”

Identification of two linear plasmids in the actinomycete Planobispora rosea

“…Interestingly, the Streptomyces chromosome is also linear (Lin et al, 1993 ;Chen et al, 1993 ;Lezhava et al, 1995 ;Leblond et al, 1996), although circular forms have been described for some deletion mutants in Streptomyces liuidans (Lin et al, 1993). All the Streptomyces linear plasmids characterized thus far share structural features : the telomeric regions are long inverted repeats from 0.6 t o 81 kb in length containing direct and inverted repeated sequences The GenBank accession numbers for the sequences reported in this paper are AF041863, AF041864 and AF041865.…”