Endoribonuclease IV. 2. Further investigation on the specificity

The poly(A)-specific endoribonuclease IV produces oligo(A) fragments of a chain length of 10 AMP nucleotides. One enzyme molecule performs 1700 cleavages per min; the cleavages occur randomly. The endoribonuclease IV is a nuclear enzyme which is present in the oviduct of quails in a concentration of 40 000 enzyme molecules per cell. Poly(A) segments on mRNA are selectively hydrolyzed by endoribonuclease IV; the poly(A)-free part of the RNA is not affected. After incubation with the enzyme, a residual oligo(A) stretch of 5 AMP nucleotides remains on poly(A)-rich RNA. The endoribonuclease IV does not disintegrate the polyribosomal complex after incubation in vitro and the enzyme has also no influence on the translational capacity of a cell-free protein-synthesizing system.