CHARACTERIZATION OF GENES ENCODING HYDROXYPYRUVATE REDUCTASE IN CUCUMBER

Several clones corresponding to the gene encoding NADH-dependent hydroxypyruvate reductase have been isolated from a cucumber genomic library. Restriction mapping indicates the presence of two HPR genes, hpr-A and hpr-B, in the cucumber genome. Examination of the DNAs of individual plants suggests that hpr-A and hpr-B are most likely alleles at a single locus. The sequence of a 6.7 kb genomic fragment that includes the entire transcribed region, 2.2 kb of 5' flanking sequence, and about 0.8 kb of 3' flanking sequence reveals the presence of 12 introns in hpr-A. These introns are AT-rich relative to the exons. The donor sequence at the 5' end of the sixth intron contains an unusual dinucleotide, GC, rather than the nearly invariant GT. Primer extension analysis maps the transcription initiation site to 61 nucleotides upstream of the translation initiation codon. An AT-rich stretch is centered at position -31 with respect to the transcription initiation site, and a potential CCAAT box is centered at position -138. Several elements that are homologous to regulatory elements of other plant genes have been identified in the flanking regions of hpr-A.