Summary auto-generated
This study identified and characterized two linear plasmids, pPR1 (27.5 kb) and pPR2 (16 kb), in Planobispora rosea, an actinomycete that produces the antibiotic GE2270. The plasmids were confirmed to be linear through restriction analysis and exhibited structural features similar to Streptomyces linear replicons. Both plasmids have 5' ends protected by terminal proteins, as demonstrated by resistance to λ exonuclease digestion. The plasmids share an internal homologous region containing open reading frames with similarity to recombination and DNA repair proteins. The pPR2 telomeric regions consist of approximately 650 nucleotide inverted repeats rich in direct and inverted repeat sequences, with a GC-rich domain containing multiple GGGGGAAC repetitions. Importantly, strains lacking both plasmids still produce and remain resistant to GE2270, indicating the antibiotic biosynthesis and resistance genes are chromosomally encoded. Southern blot analysis showed no cross-hybridization between the plasmids' telomeric regions or with chromosomal DNA, suggesting distinct evolutionary origins despite their shared genomic region.
Key findings
- Two linear plasmids (pPR1 and pPR2) were identified in Planobispora rosea with terminal proteins covalently linked to their 5' ends
- The plasmids share an internal region containing genes related to DNA recombination and repair but have distinct telomeric sequences
- pPR2 telomeres consist of ~650 nt inverted repeats rich in direct and inverted repeats, with a GC-rich domain
- Antibiotic GE2270 production and resistance are chromosomally encoded, not plasmid-associated, as strains without plasmids retain these traits
- The structural organization resembles Streptomyces linear replicons, suggesting bidirectional replication from an internal origin rather than from the ends
This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.
Abstract
Two linear plasmids (pPR1, 27.5 kb, and pPR2, 16 kb) were identified in Planobispora rosea, an actinomycete that produces the antibiotic GE2270, an inhibitor of the elongation factor Tu. Strains lacking both plasmids still produce and are resistant to GE2270. The two plasmids share an internal region of high similarity, but no cross-hybridization was detected between their telomeric regions or between plasmid and chromosomal DNA. The 5' ends of the plasmids appear to be linked to terminal proteins. The telomeric regions of pPR2 were cloned after 3'- end homopolymer tailing and PCR amplification. The approximately 650 nt telomeric DNA sequences of pPR2 are repeated in inverted orientation and are rich in direct and inverted repeats; the 350 bp terminal region is less G + C-rich than the rest of the plasmid. The structural organization of these plasmids appears to be similar to Streptomyces linear replicons.