engleski

Protein-bound DNA ends in Streptomyces rimosus

The early strain R6-65 and a later derivative R6-501 from the oxytetracycline development programme of the "Zagreb" strain of S. rimosus have been compared. The linear chromosomal restriction map of R6-501 was established in earlier work and was 8 Mb in size with terminal inverted repeats (TIR) of 550 kb. The digestion pattern of the R6-65 chromosome was indistinguishable. Previous restriction mapping with several enzymes showed that the 310 kb linear plasmid in R6-65 (pPZG102) is smaller than the 387 kb plasmid in R6-501 (pPZG101). No TIRs could be detected in pPZG102 by restriction mapping. pPZG101 appears to have been derived from pPZG102 by a recombination event that generated terminal inverted repeats of 180 kb. Restriction fragments corresponding to protein-bound linear ends were isolated and visualised in agarose gels. As had been expected from the presence of the chromosome with a TIR and pPZG102 without a TIR, R6-65 gave rise to three end fragments. Surprisingly, R6-501, in which both the plasmid and chromosome have a TIR, also gave three end fragments. From the restriction mapping, it had been expected that the end fragments in R6-501 would be identical in size to those in R6-65. However, all three of the fragments differed in size. Work is underway to assign the ends to molecules in the cell mapped by pulsed-field gel electrophoresis and to determine the nature of the changes between R6-65 and its descendant R6-501 using DNA sequencing.

Streptomyces rimosus; linear plasmid; end fragments; protein-bound linear ends

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