Differential transcription in vivo and in vitro of two adjacent maize chloroplast genes: The large subunit of ribulosebisphosphate carboxylase and the 2.2-kilobase gene

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Abstract
The transcription of cloned maize plastid DNA sequences in vitro by maize plastid DNA-dependent RNA polymerase was studied to expose the roles of the enzyme, polypeptide cofactors, and DNA sequences in the regulation of gene expression. The 4.35-kilobase pair BamHI fragment 9 carries the maize plastid gene for the large subunit of ribulosebisphosphate carboxylase and part of the gene for a 2.2-kilobase RNA. These 2 genes are separated by .apprxeq.330 base pairs and are transcribed divergently. Transcripts of the gene for the large subunit of ribulosebisphosphate carboxylase are abundant in bundle sheath cells of maize leaves and transcripts of the 2.2-kilobase RNA gene are present in both mesophyll cells and the adjacent bundle sheath cells. In vitro, in the presence of the S factor, maize chloroplast DNA-dependent RNA polymerase produces a transcript of the gene for the large subunit of ribulosebisphosphate carboxylase with a 5'' terminus like that of the corresponding mRNA isolated from plastids, transcribes chloroplast DNA sequences of Bam fragment 9 in a chimeric plasmid in preference to the vehicle RSF 1030 and, in a ratio of 3:1, preferentially transcribes the gene for the large subunit of ribulosebisphosphate carboxylase over the 2.2-kilobase RNA gene from supercoiled chimeric plasmid DNA.