The organization of the chloroplast DNA in wheat and maize in the region containing the LS gene.

The DNAs of the plasmids pTac39 and pZmB1B, which contain the wheat chloroplast DNA BamHI fragment 2 and the maize chloroplast DNA BamHI fragment 9 respectively, were analysed by electron microscopy and by Northern blotting. Both plasmids contain the gene for the large subunit of ribulose bisphosphate carboxylase (LS gene). Comparison of the DNAs of the two species by partial denaturation and heteroduplex analysis shows extended homologies interspersed with a fine pattern of non-homology. On analysis of wheat-RNA X maize-DNA hybrids a region of non-homology at the 3' end of the LS mRNA of about 200 bases was found. Analysis of wheat DNA X RNA hybrids showed that the wheat LS mRNA contains 1700 +/- 50 bases and another hybrid, containing 2400 bases was also shown to occur in a position adjacent to that formed by the LS mRNA. Binding of Escherichia coli RNA polymerase and the start of transcription in vitro occurred at well-defined sites, which are located between or close to the positions where mRNA X DNA hybrids are found. A modified technique for the preparation and fractionation by electrophoresis of glyoxalated RNA is described.