RRB1 and RRB2 encode maize retinoblastoma-related proteins that interact with a plant D-type cyclin and geminivirus replication protein.
Unlike mammalian and yeast cells, little is known about how plants regulate G1 progression and entry into the S phase of the cell cycle. In mammalian cells, a key regulator of this process is the retinoblastoma tumor suppressor protein (RB). In contrast, G1 control in Saccharomyces cerevisiae does not utilize an RB-like protein. We report here the cloning of cDNAs from two Zea mays genes, RRB1 and RRB2, that encode RB-related proteins. Further, RRB2 transcripts are alternatively spliced to yield two proteins with different C termini. At least one RRB gene is expressed in all the tissues examined, with the highest levels seen in the shoot apex. RRB1 is a 96-kDa nuclear protein that can physically interact with two mammalian DNA tumor virus oncoproteins, simian virus 40 large-T antigen and adenovirus E1A, and with a plant D-type cyclin. These associations are abolished by mutation of a conserved cysteine residue in RRB1 that is also essential for RB function. RRB1 binding potential is also sensitive to deletions in the conserved A and B domains, although differences exist in these effects compared to those of human RB. RRB1 can also bind to the AL1 protein from tomato golden mosaic virus (TGMV), a protein which is essential for TGMV DNA replication. These results suggest that G1 regulation in plant cells is controlled by a mechanism which is much more similar to that found in mammalian cells than that in yeast.
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Department of Plant and Microbial Biology, University of California, Berkeley 94720-3102, USA.
Durfee
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Miller
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Taranto
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Hanley-Bowdoin
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Zambryski
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Gruissem
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D000595:Amino Acid Sequence; D000957:Antigens, Viral, Tumor / Q000378:metabolism; D001665:Binding Sites; D018797:Cell Cycle Proteins; D016213:Cyclins / Q000378:metabolism; D004265:DNA Helicases / Q000378:metabolism*; D004268:DNA-Binding Proteins; D017343:Genes, Plant; D006801:Humans; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding; D016160:Retinoblastoma Protein / Q000737:chemistry*; D015534:Trans-Activators / Q000378:metabolism*; D003313:Zea mays / Q000235:genetics*
D000957:Antigens, Viral, Tumor; D018797:Cell Cycle Proteins; D016213:Cyclins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D010940:Plant Proteins; C107938:RRB1 protein, Zea mays; C107939:RRB2 protein, Zea mays; D016160:Retinoblastoma Protein; D015534:Trans-Activators; C045264:replication initiator protein; D004265:DNA Helicases