Mapping the mitochondrial DNA of Zea mays : Ribosomal gene localization

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Abstract
The 18S and 26S ribosomal genes on a 32.2-kilobase pair (kb) restriction map of Z. mays mitochondrial DNA were located. In a BAMHI restriction digest of mitochondrial DNA, band 4 carries all of the 26S gene, whereas band 2 carries the 18S gene sequence. We have cloned and mapped bands 2 and 4 and show that they are contiguous in the genome. The 26S sequence is at one end of the 13.7-kb fragment 4, immediately adjacent to the junction with fragment 2. The 18S sequence is located at the far end of the 17.5-kb fragment 2, about 15 kb away from the 26S gene. A 2nd region of 18S sequence homology is found on band 40. This region contains sequences that cross-hybridize with those in band 2. The nature of this apparent sequence repetition is unclear.