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19-Norspongia-13(16),14-diene-3-one (1) was isolated for the first time from a natural source, along with a series of known spongiane diterpenoids (2-11) and sesquiterpene (12) from two unidentified species belonging to the genus Spongia. The effects of 1, 4, 5, 8-12 on biosynthesis of nucleic acids and embryonic development of the sea urchin Strongylocentrotus intermedius have been studied. All the compounds inhibit sea urchin embryo development at concentration of 20 microg/mL and above and DNA biosynthesis at the dose of 10 microg/mL. The inhibitory effect of diterpenoids at least partly may be explained by the inhibition of thymidine kinase activity.

Influence of thermolabile lethal toxin of Y. pseudotuberculosis on the development of embryos of sea urchin (Strongylocentrotus intermedius) and on biosynthesis of nucleic acids in embryonic cells was studied. Thermolabile lethal toxin affected metabolic processes of cells by inhibiting DNA and RNA synthesis. It had damaging action on developing embryos of sea urchin causing morphological changes and, as a consequence, death of embryos.

The embryos of the sea urchin Strongylocentrotus intermedius possess the ability to incorporate into their DNAs 2'-deoxynucleosides together with all their bases, i.e., adenine, guanine, cytosine and thymine. This incorporation is inhibited by 3'-amino-2',3'-dideoxynucleosides with the same bases. 5'-Amino-5'-deoxynucleosides and 5'-amino-2',5'-dideoxynucleosides moderately inhibit the incorporation of [3H]2'-deoxynucleosides into the DNAs by competing with the latter, presumably at the phosphorylation stage. The most potent inhibiting effect is exerted by 2'-amino-2'-deoxynucleosides and 2'-asido-2'-deoxynucleosides; the mechanism of this inhibition is still obscure, however.

The sea urchin embryo nuclei which retained their ability to maintain the DNA synthesis in an in vitro system were isolated. The DNA synthesis isolated nuclei was shown to be an ATP-dependent process which is inhibited by low concentrations of actinomycin D, a polymerase alpha araCTP inhibitor. The newly synthesized DNA is represented by short fragments of about 4S. After addition of Ca2+, Mg2+-dependent DNAase to sea urchin embryo nuclei, the synthesis of short DNA fragments is enhanced. This stimulating effect of Ca2+, Mg2+-dependent DNAase is ATP-dependent and is observed only within a narrow range of enzyme concentrations (of the order of 1-5 units of DNAase activity per ml of incubation sample). The increase in the enzyme concentration to 10 or more units of activity results in the depression of DNA synthesis. It is concluded that DNA replication in sea urchin embryo nuclei depends on the presence of active DNAases as well as on the number of accessible initiation sites of DNA replication.