The centromere composition of multiple repetitive sequences on rice chromosome 5

The large-scale primary structure of the centromeric region of rice chromos ome 5 was analyzed, the first example in a cereal species. The yeast artifi cial chromosome (YAC) and bacterial artificial chromosome (BAC) contigs ali gned on the centromere of rice chromosome 5 (CEN5) covered a distance of mo re than 670 kb. Strong suppression of genetic recombination, one of the fea tures of a functional centromere, occurred along the contig region. The mos t remarkable feature of CEN5 is the composition of the multiple repetitive elements. Oryza-specific RCS2 short tandem repeats were clustered along les s than 100 kb at one end of the contig. At least 15 copies of the conserved domain of the 1.9 kb RCE1 centromeric repeats, which are similar to the lo ng terminal repeats (LTRs) of gypsy-type retrotransposon RIRE7, were disper sed mainly in 320 kb stretches next to RCS2 tandem clusters. Many copies of the LTR-like sequences of RIRE3 and RIRE8, another gypsy-type retrotranspo son, were also found throughout the contig. On the other hand, the gag-pol region was less conserved in the contig. These results indicate that the ri ce centromere is composed of multiple repetitive sequences with the RCS2 ta ndem cluster probably being situated as the core of a functional centromere of some hundreds of kilobases to megabases in length.