Levels of the RNA polymerases during the early larval development of Artemia.

Artemia nauplii contain three forms of RNA polymerase. RNA polymerases I and II have the common pattern of alpha-amanitin sensitivity of the eukaryotic enzymes, but RNA polymerase III is insensitive to high concentrations of the drug. The determination of the levels of the RNA polymerases during early larval development is affected by the increase of proteolytic activity during this stage, which produces the inactivation of RNA polymerases I and III in vitro. Protease B has been identified to be the enzyme responsible for the inactivation of RNA polymerase I. The culture conditions of Artemia larvae also affect the levels of the RNA polymerases. The maintenance of the larvae in the absence of food produces a decrease of RNA polymerases I and III several hours after hatching. In contrast, fed nauplii contain almost stable levels of the three forms of RNA polymerases during the studied period of larval development. The decrease of the levels of RNA polymerases I and III in starved nauplii could be the molecular mechanism responsible for the drop in RNA synthesis observed during the larval development in cultures of nauplii in the absence of an external source of food.