Ribosomal ribonucleases in avian liver during estrogen-induced vitellogenin synthesis

The ribonuclease activity associated with rooster liver ribosomes decreases and the endogenous ribosomal RNAase inhibitor becomes undetectable during estrogen-induced vitellogenin synthesis. The RNAase-catalyzed autodegradation of ribosomes in vitro is inhibited by Mg2+ and spermidine, while EDTA in low concentrations has an activating effect. Single-stranded, uridylic acid containing ribonucleotide polymers are the best substrates for the enzyme. Of the four homopolyribonucleotides, ribosomal RNAase catalyzes the degradation of poly(U), poly(A), and poly(C) in decreasing order of reactivity, while poly(G) is not degraded. Ribosomal RNAases from control and estrogen-stimulated roosters show differences in response to Mg2+, spermidine and EDTA. In addition, the reactivities of poly(U) and poly(C) as substrates using RNAases from stimulated roosters are markedly different from those obtained with the enzymes from control roosters.