A maize cDNA encoding a member of the retinoblastoma protein family: involvement in endoreduplication.
Retinoblastoma (RB-1) is a tumor suppressor gene that encodes a 105-kDa nuclear phosphoprotein. To date, RB genes have been isolated only from metazoans. We have isolated a cDNA from maize endosperm whose predicted protein product (ZmRb) shows homology to the "pocket" A and B domains of the Rb protein family. We found ZmRb behaves as a pocket protein based on its ability to specifically interact with oncoproteins encoded by DNA tumor viruses (E7, T-Ag, E1A). ZmRb can interact in vitro and in vivo with the replication-associated protein, RepA, encoded by the wheat dwarf virus. The maize Rb-related protein undergoes changes in level and phosphorylation state concomitant with endoreduplication, and it is phosphorylated in vitro by an S-phase kinase from endoreduplicating endosperm cells. Together, our results suggest that ZmRb is a representative of the pocket protein family and may play a role in cell cycle progression. Moreover, certain plant monopartite geminiviruses may operate similarly to mammalian DNA viruses, by targeting and inactivating the retinoblastoma protein, which otherwise induces G1 arrest.
Grafi
G
G
Department of Plant Sciences, University of Arizona, Tucson 85721, USA.
Burnett
R J
RJ
Helentjaris
T
T
Larkins
B A
BA
DeCaprio
J A
JA
Sellers
W R
WR
Kaelin
W G
WG
D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001483:Base Sequence; D001665:Binding Sites; D004265:DNA Helicases; D004261:DNA Replication; D018076:DNA, Complementary / Q000235:genetics*; D004268:DNA-Binding Proteins; D015723:Gene Library; D008969:Molecular Sequence Data; D005810:Multigene Family; D009856:Oncogene Proteins, Viral / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D011506:Proteins; D016160:Retinoblastoma Protein / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D012639:Seeds / Q000254:growth & development; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators; D003313:Zea mays / Q000235:genetics*
D001426:Bacterial Proteins; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D009856:Oncogene Proteins, Viral; D011506:Proteins; D016160:Retinoblastoma Protein; D015534:Trans-Activators; C045264:replication initiator protein; D004265:DNA Helicases