Homology of plasmids in strains of unicellular cyanobacteria

Abstract

Six strains of unicellular cyanobacteria were examined for the presence of plasmids. Analysis of lysates of these strains by CsCl-ethidium bromide density centrifugation yielded a major chromosomal DNA band and a minor band containing covalently closed circular plasmid DNA, as shown by electron microscopy and agarose gel electrophoresis. The sizes of the various plasmid species were determined; in each of the Synechococcus strains 6301, 6707, and 6908 two plasmid species were found with molecular weights of 5.3 x lo6 and 32.7 x 109. Synechococcus strain 7425 had two plasmids of molecular weight 5.4 x lo6 and 24 x 106. Synechococcus strain 6312 and Synechocystis strain 7005 each contained one plasmid species with molecular weight of 15.9 x 106 and 2.0 x lOg, respectively. Restriction enzyme analysis revealed identical cleavage patterns for the plasmids of identical molecular weight.

A small plasmid, pCA2.4, from the cyanobacterium Synechocystis sp. strain PCC 6803 encodes a rep protein and replicates by a rolling circle mechanism

“…These similarities and their prokaryotic nature make cyanobacteria good model systems for molecular genetic studies of chloroplasts. Many cyanobacterial strains contain endogenous plasmids of various sizes (2,6,8,28,29,31,39,40,43,(46)(47)(48)52), but thus far all of these plasmids have proven to be cryptic.Central to the genetic study of cyanobacteria has been the development of efficient cloning vectors that can transform cyanobacteria. However, the construction of these cloning and expression vectors is greatly dependent upon an understanding of DNA replication of cyanobacterial plasmids.…”

Cloning and expression in Escherichia coli K-12 of the structural gene for outer membrane PhoE protein from Enterobacter cloacae

“…Ligation with T4 DNA ligase was performed as described by Tanaka and Weisblum (1975). Analyses of plasmid DNA and DNA fragments were performed by electrophoresis in a horizontal 0.6 % agarose slab gel (Van den Hondel et al, 1979). Insertions of the transposable element y6 in plasmid pEC17 were obtained as described by Guyer (1978).…”

A new approach for molecular cloning in cyanobacteria: cloning of an anacystis nidulans met gene using a Tn 907-induced mutant

“…Plasmids (or cosmids) from E. coli and from A. nidulans R-2 strains were purified by CsClethidium bromide density gradients accordin to Davis et al (1980) and Van den Hondel et al (1979), respectively. For rapid screening of E. coli transformants, the technique devised by Birnboim and Doly (1979) was followed.…”