engleski

Characterization of two novel satellite DNAs from the mollusc Donax trunculus

Satellite DNAs, or tandemly repeated highly reiterated DNA sequences, are usually located within heterochromatic regions of chromosomes. Even though the chromosomes of the wedge shell clam Donax trunculus do not posses a significant heterochromatin component, the presence of five distinct relatively low copy number satellite DNAs in the genome has been revealed previously, and those sequences are well characterized. Two novel low copy satellite DNAs were discovered after HinfI restriction of genomic DNA, followed by cloning and sequencing. The consensus sequences of both satellites have the same monomer length, 172 bp, but are otherwise highly divergent in nucleotide sequence and even in GC content. One satellite, DTF1, is characterized by low overall sequence variability of 1.6 %, whereas within the other satellite, DTF2, two distinct, but internally also highly homogenous, sequence groups could be discerned by the presence of diagnostic mutations. Further characterization via Southern hybridization of genomic restrictions and time course analysis confirms the tandem arrangement of these sequences in the genome. The simultaneous presence of several independent low copy satellites in the genome indicates a genomic organization different to the one observed in other species and well described in tenebrionid insects. Its hallmark is the presence of single satellite DNA that comprises a significant portion of the genome, whereas additional satellites are present in a low number of copies. These two organizational patterns can, however, be linked via the hypothesis stipulating that the related species share a “library” of conserved satellite DNAs, some of which can then be amplified to become a major satellite. Since it is probable that the pattern observed in D. trunculus represents a state in the absence of the amplification of a major satellite, further study of such organization promises to help us gain insight into processes that guide evolution of satellite DNAs within a genome.

satellite DNA; heterochromatin; mollusc

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