A Unique Repetitive DNA Sequence in the

We found a novel type of repetitive DNA sequence in the Myxococcus xanthus genome. The first repetitive sequence is located in the spacer region between the ops and tps genes. We cloned five other repetitive sequences using the first repetitive sequence as a probe and determined their nucleotide sequences. Comparison of these sequences revealed that the repetitive sequences consist of a 87-bp core sequence and that some clones share additional homology on their flanking regions. In prokaryotic genomes a variety of repetitive DNA sequences are found (for a review, see reference 6). First are duplicated genes, such as the seven rrn genes for rRNA present in the Escherichia coli genome, and many closely related genes, presumably derived from common ancestral genes. Second are insertion sequences and transposons. For example, 7 copies of IS], 12 copies of IS2, and 6 copies of IS3 are found in the genome of E. coli K-12 W3110 (9). Third are recognition sequences bound by various sequence-spe-cific DNA-binding proteins and other repetitive sequence