AN ORDERED YEAST ARTIFICIAL CHROMOSOME LIBRARY COVERING OVER HALF OF RICE CHROMOSOME-6

Yeast artificial chromosome (YAC) clones carrying DNA marker sequences located on the rice genetic map of chromosome 6 were ordered for phys ical mapping. A total of 122 restriction fragment length polymorphism markers, 16 sequence-tagged site markers, and five random amplified po lymorphic DNA markers located, on average, at 0.9-cM intervals, were u sed for YAC clone screening by colony/Southern hybridization and PCR s creening, respectively. A total of 216 individual YACs were selected f rom our YAC library of 7000 clones covering six genome equivalents. Ea ch DNA marker could select, on average, 4.8 YAC clones, with 11 clones being the maximum. The YACs localized to the corresponding linkage ma p positions form 43 contigs and encompass about 60% of rice chromosome 6. This is the first step in constructing a physical map covering the whole rice genome by chromosome landing with YAC clones. These YACs a nd data will be used soon to isolate phenotypical trait genes by map-b ased cloning.