The centromere composition of multiple repetitive sequences on rice chromosome 5.

The large-scale primary structure of the centromeric region of rice chromosome 5 was analyzed, the first example in a cereal species. The yeast artificial chromosome (YAC) and bacterial artificial chromosome (BAC) contigs aligned on the centromere of rice chromosome 5 (CEN5) covered a distance of more than 670 kb. Strong suppression of genetic recombination, one of the features of a functional centromere, occurred along the contig region. The most remarkable feature of CEN5 is the composition of the multiple repetitive elements. Oryza-specific RCS2 short tandem repeats were clustered along less 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 long terminal repeats (LTRs) of gypsy-type retrotransposon RIRE7, were dispersed mainly in 320 kb stretches next to RCS2 tandem clusters. Many copies of the LTR-like sequences of RIRE3 and RIRE8, another gypsy-type retrotransposon, were also found throughout the contig. On the other hand, the gagpol region was less conserved in the contig. These results indicate that the rice centromere is composed of multiple repetitive sequences with the RCS2 tandem cluster probably being situated as the core of a functional centromere of some hundreds of kilobases to megabases in length.