CLONING AND CHARACTERIZATION OF A CENTROMERE-SPECIFIC REPETITIVE DNA ELEMENT FROM SORGHUM-BICOLOR

A 823-bp Sau3AI fragment (pSau3A10) was subcloned from a sorghum bacte rial artificial chromosome (BAC) clone, 13I16, that contains DNA seque nces specific to the centromeres of grass species. Sequence analysis s howed that pSau3A10 consists of six copies of an approximately 137-bp monomer. The six monomers were organized into three dimers. The monome rs within the dimers shared 62-72% homology and the dimers were 79-82% homologous with each other. Fluorescence in situ hybridization (FISH) analysis indicated that the Sau3A10 family is present only in the cen tromeres of sorghum chromosomes. Sequencing, Southern hybridization, a nd Fiber-FISH analyses indicated that the Sau3A10 family is tandemly a rranged and is present in uninterrupted stretches of up to at least 81 kb of DNA. Slot-blot analysis estimated that the Sau3A10 family const itutes 1.6-1.9% of the sorghum genome. The long stretches of Sau3A10 s equences were interrupted by other centromeric DNA elements. Southern analysis indicated that the Sau3A10 sequence is one of the most. abund ant DNA families located in sorghum centromeres and is conserved only in closely related sorghum species. Methylation experiments indicated that the cytosine of the CG sites in sorghum centromeric regions is ge nerally methylated. The structure and organization of the Sau3A10 fami ly shared similarities with centromeric DNA repeats in other eukaryoti c species. It is suggested that the Sau3A10 family is probably an impo rtant part of sorghum centromeres.