A.Mapping of ct-DNA and location of genes for the ...
The Smal and BamHI restriction sites in N.otophora of ct-DNA were mapped based on the data from the following：①primary digestion：ct-DNA was digested with Smal and BamHI，individually or in combination；② secondary digestion：each Smal fragment was digested with BamHI or vice versa；③DNA hybridization of Smal fragments with BamHI fragments；④available information on Smal sites mapped or N.tabacum［16］；⑤comparison of Smal and BamHI restriction patterns from different species of Nicotiana.From the results of the mapping procedures we determined that N.otophora is 160 kb in length.The inverted repeats are 22.5 kb in length separated by a small（26 kb）and a large（89 kb）single copy region.
The 16s，23s and 5s rRNA genes of N.tabacum have been identified to reside on EcoRI fragments 8，4 and 29，respectively［17，18］.These fragments were used as probes to locate rRNA genes in N.otophora ct-DNA.The rRNA genes were proved to be located in the inverted repeats（Bam 11，5 and Sma 4，11，14），the same as was discovered in other plants［8，19，20］.Similarly，the gene for the LS was identified in the large single copy region（EcoR 4，Sma I and Bam 20，24）by hybridization using a spinach RuBPCase LS gene as the probe.All of these structural features of N.otophora ct-DNA are similar to that of N.tabocum［16，21，22］and other plants，indicating these major chloroplast genes are highly conserved in terms of their location in ct-DNA.(https://www.daowen.com)
