CLONING AND CHARACTERIZATION OF A FISH CENTROMERIC SATELLITE DNA

A highly repetitive DNA sequence family from the genome of Sparus aura ta has been cloned and characterized. The family is composed of repeat units of 186 bp in length, and it accounts for 2% of the fish genome. Data from Southern blots and in situ hybridization demonstrate that r epeating units are tandemly arranged at the centromeres of all the chr omosomes in this species. The repetitive sequence is AT rich (67%) and is characterized by short stretches of consecutive AT base pairs and by short direct and inverted repeats. Sequence analysis of six cloned monomers of the family reveals some variation among clones at random p ositions and also distinguishes two subfamilies of repeats that differ in a highly divergent block of 31 bp. These two subfamilies do not se em to be located in separate domains but occur together in the centrom ere of each chromosome pair. The presence of this repeat family in the genome of other Sparidae species, some of which are relatively distan t from S. aurata, indicates that this repetitive sequence could be an important component of the centromere in this fish family.