Protein synthesis in Artemia salina embryos : II. Resumption of RNA and protein synthesis upon cessation of dormancy in the encysted gastrula

Abstract

A study has been made of the onset of RNA and protein synthesis in encysted gastrulae of the brine shrimp, Artemia salina, during their transition from an ametabolic (cryptobiotic) state to active life and renewed embryonic development. Discrete sedimentation classes of polyribosomes in very small amounts were demonstrated in extracts from dried and prehydrated (0°C) gastrulae by sucrose density-gradient centrifugation. An increase in polyribosome content occurs within 3 minutes after dormancy is terminated in prehydrated gastrulae, and within 30 minutes in gastrulae incubated from the dried state. The rate of incorporation of 14C-labeled leucine and phenylalanine into protein in vitro by preparations from dormant gastrulae is very low but increases markedly when metabolism is resumed, paralleling the increase observed in the polyribosome content of these preparations. Polyuridylic acid stimulates (120-fold) the incorporation of phenylalanine by ribosome preparations from dormant gastrulae; the extent of this stimulation appears to fluctuate during the resumption of development. Incorporation into RNA is roughly linear in gastrulae during the first 2 hours of incubation at 30°C using NaH 14CO 3 as labeled precursor. Most of the incorporated radioactivity is associated with the two major classes of ribosomal RNA (17 S and 26 S) and 4 S RNA. The presence of RNA of high molecular weight undergoing rapid turnover is indicated by the distribution of radioactivity and absorbance below the 26 S RNA peak of sucrose gradient profiles.