A maize ribosome-inactivating protein is controlled by the transcriptional activator Opaque-2.
Although synthesis of the cytosolic maize albumin b-32 had been shown to be controlled by the Opaque-2 regulatory locus, its function was unknown. We show here that b-32 is a member of the large and widely distributed class of toxic plant proteins with ribosome-inactivating activity. These ribosome-inactivating proteins (RIPs) are RNA N-glycosidases that remove a single base from a conserved 28S rRNA loop required for elongation factor 1 alpha binding. Cell-free in vitro translation extracts were used to show that both maize and wheat ribosomes were resistant to molar excesses of b-32 but not to the dicotyledonous RIP gelonin. We extracted RIP activity from kernels during seed maturation and germination. The amount of RIP activity increased during germination, although the amount of b-32 protein remained fairly constant. Expression of a maize RIP gene under the control of an endosperm-specific transcriptional regulatory may be an important clue prompting investigation of the biological basis for RIP expression in seeds of other plants.
Bass
H W
HW
Department of Botany, North Carolina State University, Raleigh 27695.
Webster
C
C
OBrian
G R
GR
Roberts
J K
JK
Boston
R S
RS
D000595:Amino Acid Sequence; D015870:Gene Expression; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D010944:Plants / Q000235:genetics* / Q000378:metabolism; D012339:RNA, Ribosomal, 28S / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid; D015533:Transcriptional Activation; D003313:Zea mays / Q000235:genetics / Q000378:metabolism
C070555:B-32 protein, Zea mays; D010940:Plant Proteins; D012339:RNA, Ribosomal, 28S