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Many laboratories have made use of plasmids designed to facilitate the transfer of DNA by conjugation from E.coli into cyanobacteria, plasmids that were constructed in Peter Wolk's lab in the late 1980's and early 1990's. The most widely used, pRL528, carries genes encoding methylases that can protect transferred DNA from restriction by AvaI and AvaII. More recently, plasmid pRL623 has added protection against AvaIII. Those who have used these plasmids have never had an article to cite, one that described the plasmids' construction... until now! Finally, Wolk's lab has published an article that relates the properties of helper plasmids that permit efficient conjugation into Anabaena PCC 7120. Those inclined may cite: Elhai et al (1997) J Bacteriol 179:1998-2005. The article may serve also as a reference for pRL443, a kanamycin-sensitive derivative of RP4 used by many as a conjugal plasmid.