CLUSTERS OF INTERSPERSED REPEATED DNA-SEQUENCES IN THE RICE GENOME (ORYZA)

We have characterized a repeated DNA sequence (RTL122) from rice (Oryz a sativa L.) with respect to its organization in the rice genome and i ts distribution among rice and other plants. The results indicate that the RTL122 sequence is interspersed in the rice genome and limited to the genus Oryza. It is highly polymorphic and can be used to fingerpr int rice varieties. A structure was observed in which several repeated sequences were clustered in DNA regions of 15-20 kb. We characterized three bacteriophage lambda clones that contained the RTL122 sequence. Southern analysis using probes derived from restriction fragments of the three lambda clones indicated that all fragments except one are in terspersed repeated sequences and belong to different repeated sequenc e families. Subsequent slot blot hybridization showed that most of the m are only present within the genus Oryza. Some of the Oryza-specific, physically linked sequences show the same phylogenetic distribution, which suggests that these sequences might have evolved in a coordinate fashion. On the other hand, some of the repeated sequences have a dif ferent distribution even though they are physically adjacent in the ge nome. We speculate that such blocks of interspersed repeated sequences may serve as hotspots for rapid changes in the rice genome.