期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1974
卷号：71
期号：6
页码：2515-2519
DOI：10.1073/pnas.71.6.2515
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The DNA of the thermosensitive R factor, Rts1, has been examined by the technique of sedimentation in alkaline sucrose density gradients. Rts1 DNA was found as closed covalent circles in only a few copies per cell in an Escherichia coli host at the permissive temperature. Rts1 DNA appears to be synthesized at the nonpermissive temperature, but was not found as closed covalent circles. However, circular DNA could be recovered upon shift down to the permissive temperature. The large number of plasmid-negative cells which accumulate after prolonged culture at non-permissive temperature may be due to a strong selective pressure favoring the growth of rare R- segregants.
关键词：plasmid ; circularization of DNA ; curing ; alkaline sucrose
