A RIBOSOMAL 5S RIBOSOMAL-RNA-BINDING PROTEIN GENE FROM RICE (ORYZA-SATIVA L.) IS REGULATED IN A CELL-CYCLE PHASE-SPECIFIC MANNER AND IN RESPONSE TO GIBBERELLIN

Transcripts of a ribosomal 5S rRNA-binding protein from rice (Oryza sa tiva L.), RL5, were shown to accumulate in internodes of deepwater ric e after treatment with the growth-promoting hormone gibberellin (GA). Induction of RL5 expression by GA in the rice internode was limited to the intercalary meristem and to the lower half of the elongation zone . Expression of RL5 was induced in G1 phase of the cell cycle and redu ced in abundance during S phase and again during mitosis. These result s indicate that RL5 expression is highest in proliferating cells and i s induced by mitotic stimulation. However, transcript levels are not c onsistently high in proliferating cells, but, instead, they are highly regulated during passage of cells through the different phases of the cell division cycle.