Maize phosphoenolpyruvate carboxylase involved in C4 photosynthesis: nucleotide sequence analysis of the 5' flanking region of the gene.

To clone the genomic DNA fragment containing the putative promoter region of the gene for phosphoenolpyruvate carboxylase [EC 4.1.1.31] involved in C4 photosynthesis (C4-type PEPC), maize genomic libraries were screened. On probing with a 384-bp fragment from the N-terminal coding region of the maize cDNA for C4-type PEPC, four EcoRI-fragments differing in the restriction map were cloned, reflecting the presence of a small gene family. Southern blot analyses were carried out on the genomic DNA and the cloned DNA fragments using several segments of the cDNA for C4-type PEPC as probes. The results indicated that the C4-type PEPC is encoded by a single gene and the cloned 7.0-kb fragment was derived from this gene. The transcription start site, as determined in a primer extension experiment, was located at about 4 kb downstream of the 5' end of the cloned fragment. The nucleotide sequence was determined for the region which extended about 1 kb upstream from the transcription start site and possible signal sequences related to gene expression were found, including four classes of direct repeats. The sequences of the corresponding regions of the other two cloned fragments (8.9 and 12.9 kb) which strongly hybridized with the 384-bp probe were very similar to each other, but they were quite different in the 5' upstream region from the sequence of the gene for C4-type PEPC.