Repetitive sequences of the sea urchin genome: III. Nucleotide sequences of cloned repeat elements

Abstract

The nucleotide sequences of eight randomly selected, cloned, repetitive sequence elements were determined. No homologies exist among the eight sequences that are sufficient to promote cross-reaction between them under standard conditions of measurement. Thus, each sequence is representative of a different repeat sequence family. Statistically significant but short (8 to 41 nucleotides) internal direct and inverse repetitions occupy a minor fraction of the sequence length in five of the eight repeat sequences. None contains internal reverse repeats sufficiently long to permit inclusion in the “foldback” DNA fraction. The general lack of internal sequence homology means that the sequence complexity of the eight clones is approximately equal to the length of the cloned inserts. Nucleotide sequences of three different members of one particular short interspersed repeat sequence family are also reported. Comparison of these sequences reveals that both the number and order of internal sequence subelements differ among family members. The results show that both fine-scale rearrangement and sequence divergence have occurred during the evolution of this repeat family.