Identification of two families of satellite-like repetitive DNA sequences from the zebrafish (Brachydanio rerio).

To further our understanding of the structure and organization of the zebrafish genome, we have undertaken the analysis of highly and middle-repetitive DNA sequences. We have cloned and sequenced two families of tandemly repeated DNA fragments. The monomer units of the Type I satellite-like sequence are 186 bp long, A+T-rich (65%), and exhibit a high degree of sequence conservation. The Type I satellite-like sequence constitutes 8% of the zebrafish genome, or approximately 8 x 10(5) copies per haploid genome. Southern analysis of genomic DNA, digested with several restriction endonucleases, shows a ladder of hybridizing bands, consistent with a tandem array, and suggests longer range periodic variations in the sequence of the tandem repeats. The Type II satellite has a monomer length of 165 bp, is also A+T-rich (68%), and constitutes 0.2% of the zebrafish genome (22,000 copies per haploid genome). Southern analysis reveals a complex pattern rather than a ladder of regularly spaced hybridizing bands.