GENOMIC ORGANIZATION OF 57 RIBOSOMAL-PROTEIN GENES IN RICE (ORYZA-SATIVA L) THROUGH RFLP MAPPING

Four hundred cDNA clones from rice (Oryza sativa L.) callus and root c DNA libraries, with a high similarity to about 70 kinds of ribosomal p roteins (r-protein) in eukaryotic as well as prokaryotic organisms, we re identified by their deduced amino acid sequences. Southern hybridiz ation of 114 independent cDNA clones with total rice genomic DNA showe d 77 distinct and specific hybridization patterns. Of the 77 clones re presenting the above hybridization patterns, copies of 67 clones corre sponding to 57 r-proteins could be estimated and, among these, only 6 clones were single copy, indicating that almost 90% of these r-protein s in rice were encoded by small multigene families. Loci of 36 r-prote in genes could be mapped on the rice linkage map by using 30 full-leng th cDNA clone sequences from specific RFLP bands. Another 21 expressed gene loci were mapped using 3' untranslated region specific cDNA prob es amplified from the multicopy cDNA clones representing 17 of the r-p rotein multicopy gene families. The above 57 gene loci were mapped fro m 51 cDNA clones and 41 of these r-protein genes mapped to regions tha t did not show any clustering, while in 5 cases, pairs of r-protein ge nes cosegregated or linked closely. The r-protein genes in rice were l ocated throughout the 12 chromosomes and it was found that more than o ne copy within a multigene family may be expressed simultaneously.