ANALYSIS OF CLONES CARRYING REPEATED DNA-SEQUENCES IN 2 YAC LIBRARIESOF ARABIDOPSIS-THALIANA DNA

YAC clones carrying repeated DNA sequences from the Arabidopsis thalia na genome have been characterized in two widely used Arabidopsis YAC l ibraries, the EG library and the EW library. Ribosomal, chloroplast an d the paracentromeric repeat sequences are differentially represented in the two libraries. The coordinates of YAC clones hybridizing to the se sequences are given. A high proportion of EG YAC clones were classi fied as containing chimaeric inserts because individual clones carried unique sequences and repetitive sequences originating from different locations in the genome. None of the EW YAC clones analysed were chima eric in this way. YAC clones carrying tandemly repeated sequences, suc h as the paracentromeric or rDNA sequences, exhibited a high degree of instability. These observations need to be taken into account when us ing these libraries in the development of a physical map of the Arabid opsis genome and in chromosome walking experiments.