IDENTIFICATION OF THE DUPLICATED SEGMENTS IN RICE CHROMOSOME-1 AND CHROMOSOME-5 BY LINKAGE ANALYSIS OF CDNA MARKERS OF KNOWN FUNCTIONS

We mapped two loci for ADP-ribosylation factor homologues (ARF1, ARF2) and two loci for cysteine proteinase inhibitors (oryzacystatin-I and -II: OCI, OCII) by linkage analysis of restriction fragment length pol ymorphism loci in rice (Oryza sativa L.) genomic DNAs using their cDNA s as probes. Oc-l and Arf-2 were found to be closely located to each o ther on chromosome 1, while Oc-2 and Arf-1, both found on chromosome 5 , were also located close to each other. The map distances are about 2 cM in both pairs. In each chromosome, the Arflocus was located al,out 27 cM from that of the aldolase gene (Ald-2 in chromosome 1 and Ald-l in chromosome 5). These three genes are in the same order, Ald-Arf-Oc , but in opposite orientations relative to the distal ends of the link age group. The presence of two sets of three linked genes on chromosom es 1 and 5 strongly suggests a structural similarity of the blocks of the two chromosomes, which probably reflects duplication of the segmen t. A recent investigation by other workers has shown that these rice b locks correspond to two regions in maize chromosomes 8 and 6, that hav e previously been shown to share many duplicated nucleotide sequences. It is therefore very likely that the duplication of the region occurr ed before the divergence of rice and maize during the evolution of the subfamilies of the grasses (Gramineae). In view of a recently discove red possible structural similarity between the small GTP-binding prote in superfamily, which includes Arf and ras proteins, and the cystatin family, the close linkage of Oc and Arfloci found in the present study suggests a possible cluster of genes related to the small GTP-binding proteins.