[Relation between changes in the palindromic fraction and DNA replication during early stages of sea urchin development].

Inverted repeat DNA sequences during embryogenesis were tested by comparing the bulk inverted repeat taken from Strongylocentrotus intermedius sea urchin embryos at different stages of development. This fraction exhibited quantitative and qualitative changes. A reversible quantitative decrease was associated with the 16-cell embryo and blastula stages. Sizing on 1.5% agarose gel indicated that the length of the palindromic sequences at the early blastula stage was predominantly about 200 b. p., and at the pluteus stage 240 b. p. Sensitivity of the palindromic sequences to S1 nuclease digestion at the blastula and gastrula stages was different. It was shown that a specific set of the inverted repeats was included in fragments of DNA--comparising the origin of replication. The results suggest that the change of inverted repeats may be determined by replication processes.