Characterization of all the subunits of replication factor C from a higher plant, rice (Oryza sativa L.), and their relation to development.

Replication factor C (RFC), which is composed of five subunits, is an important factor involved in DNA replication and repair mechanisms. Following previous studies on the RFC3 homologue from rice (Oryza sativa L. cv. Nipponbare) (OsRFC3), we succeeded in isolating and characterizing one large and three small subunits of RFC homologues from the same rice species and termed them OsRFC1, OsRFC2, OsRFC4 and OsRFC5. The plant was found to have all RFC subunits known in yeasts, human and other eukaryotes. The open reading frames of OsRFCs encoded a predicted product of 1021 amino acid residues with a molecular mass of 110.8 kDa for OsRFC1, 339 amino acid residues with a molecular mass of 37.4 kDa for OsRFC2, 335 amino acid residues with a molecular mass of 36.8 kDa for OsRFC4, and 354 amino acid residues with a molecular mass of 40.5 kDa for OsRFC5. All the OsRFC subunits have highly conserved amino acid motifs among RFC proteins, RFC box, and an unrooted phylogenetic tree shows each OsRFC subunit belongs to each RFC subunit group. These subunits showed differences in their expression patterns among tissues. The transcripts of OsRFCs were expressed strongly in the proliferating tissue, the shoot apical meristem (SAM), and very weakly in the mature leaves which have no proliferating tissues. However, in young leaves and flag leaves, tissue-specific expression of OsRFC3 and OsRFC4 was shown. On the other hand, cell cycle arrest by cell cycle inhibitors resulted in significant differences in OsRFC expression patterns. These results suggest the functional differences of each OsRFC subunit in tissues and the plant cell cycle. The roles of these molecules in plant DNA replication and DNA repair are discussed.