NUCLEAR-CYTOPLASMIC TRANSLOCATIONS OF PROTEIN P26 DURING AEROBIC-ANOXIC TRANSITIONS IN EMBRYOS OF ARTEMIA-FRANCISCANA

Embryos of the crustacean Artemia franciscana survive continuous anoxi a for periods of years, during which their metabolism comes to a rever sible standstill. A question of some interest concerns the maintenance of cellular integrity in the absence of biosynthesis and an ongoing e nergy metabolism. The present paper continues previous work on an abun dant protein (p26) that undergoes extensive intracellular translocatio n during aerobic-anoxic transitions, exhibits several characteristics of stress proteins, and might be involved in metabolic regulation duri ng aerobic-anoxic transitions. Since it has been established that intr acellular pH (pH(i)) plays a major role in aerobic-anoxic transitions in this system we examined the pH-dependence of nuclear-cytoplasmic tr anslocations of p26. In unincubated and aerobic-incubated embryos (pH( i) greater than or equal to 7.9) p26 was located in the ''soluble'' fr action, whereas in anoxic embryos (pH about 6.3) roughly 50% was trans located into the nucleus as shown by immunocolloidal gold electron mic roscopy. These nuclear translocations also took place in vitro, simply by manipulating buffer pH in a physiologically appropriate fashion. I mmunostaining of Western blots prepared after two-dimensional electrop horesis revealed several isoforms of native p26. The isoelectric point of the major isoform was 7.10 +/- 0.05, a value close to the pH at wh ich p26 translocation into the nucleus was first initiated in vitro. P -31-NMR measurements indicated that pH(i) was maintained at acidic lev els (about 6.3) during prolonged anoxia. We also found that pH(i) of h ydrated (0 degrees C) but otherwise unincubated embryos was alkaline, allowing for rapid resumption of metabolism under permissive condition s. The significance of these pa-dependent translocations of p26 is dis cussed. (C) 1995 Academic Press, Inc.