Summary: A procedure was developed for the isolation of heterocysts from cyanobacterial filaments without recourse to mechanical disruption of the vegetative cells. DNA was then extracted from purified heterocysts by heating with 2% (w/v) SDS at 70 °C for 10 min. Following purification, this DNA was used for treatment with a range of restriction endonucleases and the results compared with DNA isolated from vegetative cells. Both heterocyst and vegetative DNAs from PCC 7120 and CA (ATCC 33047) were cut by I, dIII, RI, I, II and I. However, none of the DNAs were cut by I, I or I, indicating that the DNA from both organisms is methylated, but that no gross changes in methylation occur during heterocyst formation. Treatment of the DNAs with the former enzymes, followed by separation of the fragments by agarose gel electrophoresis, resulted in most cases in patterns of bands, which allowed a limited comparison of heterocyst and vegetative DNAs. No major differences were seen between the heterocyst and vegetative DNAs of either organism, implying that there are unlikely to be extensive rearrangements or major loss of DNA during heterocyst differentiation.


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