Diadenosine 5',5'"-P1,P4-tetraphosphate in developing embryos of Artemia

Diadenosine 5',5'"-P1,P4-tetraphosphate (Ap4A) has been detected in cysts and developing embryos of the brine shrimp Artemia in amounts 10(4)-10(6) times lower than that of the guanine analogue, Gp4G. The unexpectedly high level of Ap4A in dormant cysts of 2.37 pmol/10(6) cells can be reduced to 0.03 pmol/10(6) cells by decapsulation and storage in saturated NaCl. When development is reinitiated, the Ap4A content of the decapsulated embryos undergoes a rapid 125 -fold increase, reaching a maximum of 3.79 pmol/10(6) cells at the point of emergence when DNA replication begins. If replication is delayed by hypoxia, the Ap4A level is adjusted in order to reach the same maximum value when replication finally begins. As replication proceeds, the level of Ap4A declines again. Unlike mammalian cells, Ap4A in Artemia is less metabolically labile than ATP. These results are consistent with the suggested role of Ap4A in the initiation of DNA synthesis.