Properties of two cryptic plasmids found in the cyanobacterium Anacystis nidulans
Bartkus, Joanne Martha, 1954-
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Plasmid deoxyribonucleic acid (DNA) was isolated from Anacystis nidulans cells labeled with [³H]deoxyadenosine by preparative equilibrium density gradient centrifugation using ethidium bromide-cesium chloride gradients. Neutral sucrose velocity gradient centrifugation (5-20%) showed two major peaks of radioactivity with sedimentation coefficients of 24 and 48S as calculated by a computer program. This material was shown to be covalently closed circular (CCC) DNA by conversion to open circular (OC) material with decreased S values by ionizing radiation. Molecular weights of the CCC DNA molecules were determined from the S values to be 4.5 x 10⁶ daltons and 22.9 x 10⁶ daltons. Guanine + cytosine content was determined by analytical cesium chloride equilibrium density gradient centrifugation to be 60.2 and 53.06 moles % for the two plasmids. The plasmids were resistant to elimination in cultures treated with a variety of curing agents.