PROXIMAL PROMOTER REGION OF THE WHEAT HISTONE H3 GENE CONFERS S-PHASE-SPECIFIC GENE-EXPRESSION IN TRANSFORMED RICE CELLS

The cis-regulatory elements that confer cell cycle-dependent expression to the wheat histone H3 gene were investigated in rice cells (Oc strain) transformed with H3/GUS chimeric genes. 5' deletion mutants of the H3 promoter region (from - 1711, - 908 or - 185 to + 57 relative to the transcription start site) were joined to the coding sequence of the bacterial beta-glucuronidase (GUS) gene then introduced stably into rice cells. S1 analyses of the RNA from transformed rice cells whose cell cycles had been synchronized by treatment with aphidicolin showed that the steady-state levels of the transcripts from chimeric genes were altered with the change in DNA synthesis and the content of rice H3 mRNA throughout the cell cycle. Even though H3 promoter activity decreased as 5' deletion proceeded, transcripts from the chimeric genes showed increases, as much as 10-fold 1 h after release from the aphidicolin block, which were rapidly lost over the next 4 h. The results suggest that the 242 bp sequence from - 185 to + 57, which contains the basal promoter region, confers the S phase-specific expression of the H3 gene and that the upstream sequence from position - 186 is required for the full activity of this promoter.