Adenylation and ADP-ribosylation in the mouse 1-cell embryo

The incorporation of [3H]AAadenosine into cold trichloroacetic acid (TCA) insoluble material by the mouse 1-cell embryo has been studied. Incorporation of label was high immediately after fertilization, then decreased over the next 7 h with the sharpest decline occurring 3-5 h after fertilization. A small maximum was observed at the time of pronuclear DNA synthesis. Actinomycin D at a concentration which inhibited the cleavage of 1-cell embryos by 50% had little effect on this incorporation, which in the period 1-6 h post-fertilization was shown by autoradiography to be confined to the ooplasm of the newly fertilized ovum. [3H]Adenosine and poly ([3H]A) were released from embryo RNA labelled 1-3 h after fertilization with [3H]adenosine by digestion with a mixture of ribonucleases A and T1. The poly ([3H]A) segments were hydrolysed by alkali to 3'-[3H]AMP and [3H]adenosine ([3H]AMP/[3H]adenosine = 5/1), and by snake venom phosphodiesterase to 5'-[3H]AMP but very little [3H]adenosine. These results suggest that adenylation of RNA occurs soon after fertilization, that this is a cytoplasmic event, and that most of the newly synthesized poly ([3H]A) segments are joined to pre-existing poly (A) tracts. The unusual polynucleotide, poly (ADP-ribose), identified by its resistance to alkali and the release of 2'-(5''-phosphoribosyl)-5'[3H]AMP on incubation with snake venom phosphodiesterase, was also found in the ribonuclease digest.