Preservation of a complex satellite DNA in two species of echinoderms.
The cloning and sequencing of a tandemly arrayed repetitive DNA sequence from the sea cucumber Holothuria tubulosa has been recently described (Sainz, J., Azorín, F. and Cornudella, L. 1989. Gene 80, 57-64). We have now searched the genomes of several echinoderm species for the presence of homologous repetitive elements. A close but not identical repeated sequence has been identified in a related holothuroid, H. polii. The monomeric repeat unit is 391 bp long and has a base composition of 66.8% A and T residues, lined up in tracts of 4 nt or larger. The monomeric sequence lacks any internal subrepeat organization although it displays a substantial degree of internal redundancy in the form of inverted and direct repeats. The repeated element accounts for 0.34% of the genome which corresponds to a repetition frequency of about 0.5 x 10(5) copies per haploid complement. The intra- and interspecific homologies among monomers of the satellite DNA as derived from sequence analyses are very high, averaging 97%. The results suggest that the homogeneity of the highly reiterated DNA sequence may be attributed to evolutionary conservative trends.
Sainz
J
J
Unidad de Química Macromolecular del CSIC, Universitat Politècnica de Catalunya, Barcelona, Spain.
Cornudella
L
L
D000818:Animals; D001483:Base Sequence; D015139:Blotting, Southern; D004276:DNA, Satellite / Q000235:genetics*; D004447:Echinodermata / Q000235:genetics*; D005796:Genes; D008297:Male; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D012091:Repetitive Sequences, Nucleic Acid; D012616:Sea Cucumbers / Q000235:genetics; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity
D004276:DNA, Satellite