Degradation of RNA in rat reticulocytes. I. Purification and properties of rat reticulocyte RNase

Purification and characterization of two ribonucleases from human erythrocytes: immunological and enzymological comparison with ribonucleases from human urine

Two ribonucleases (RNases), one active against RNA as well as poly(C) and the other more markedly against poly(C), were isolated from human erythrocytes by acetone fractionation in the presence of 0.25 M H2SO4, followed by a series of column chromatographies. The purified enzymes appeared homogeneous as judged by sodium dodecyl sulfate--polyacrylamide gel electrophoresis (SDS-PAGE), and were tentatively designated RNase HE-1 and RNase HE-2. The content of RNase HE-1 in erythrocytes was much higher than that of RNase HE-2. The molecular mass of RNase HE-1 was determined to be 18,000 and 16,000 Da, and that of RNase He-2 39,000 and 31,000 Da, by SDS-PAGE and gel filtration, respectively. The catalytic properties and structural features of RNase HE-1 including the amino acid composition and N-terminal amino acid sequence indicated that its protein moiety is strictly related to a nonsecretory RNase purified from human urine (Yasuda et al., 1988, Biochim. Biophys. Acta 965, 185-195). In particular, the N-terminal amino acid sequence up to the 32nd residue was identical with that of urine nonsecretory RNase reported recently (Beintema et al., 1988, Biochemistry 27, 4530-4538). Furthermore, RNase HE-1 was immunologically indistinguishable from urine nonsecretory RNase, but clearly differed from urine secretory RNase. On the other hand, erythrocyte RNase HE-2 was enzymologically and immunologically similar to urine secretory RNase.

Activation of latent RNAase by antibodies against rat liver RNAase inhibitor

RNAase inhibitor was purified to homogeneity from rat liver. The purified inhibitor was identified by measuring the activity in gel slices after polyacrylamide gel electrophoresis under non-denaturing conditions. Antibodies were prepared by immunization of guinea pigs with the inhibitor. The antibodies formed single precipitin lines with free RNAase inhibitor and RNAase A-inhibitor complex that fused in a micro-Ouchterlony test. Partially purified IgG from immunized animals, but not control animals, inhibited the activities of the free inhibitor and the inhibitor in the complex. In the latter case, the RNAase-inhibitor complex was dissociated and active RNAase was liberated.

Activation of latent ribonuclease in the fat-body of fleshfly (Sarcophaga peregrina) larvae on pupation

A crude extract of the fat-bodies of third-instar larvae of Sarcophaga peregrina (fleshfly) was found to contain latent RNAase (ribonuclease) consisting of RNAase and inhibitor protein that is sensitive to p-chloromercuribenzoic acid. The RNAase activity in the crude extract of fat-bodies became detectable with time after puparium formation, indicating that the inhibitor is selectively inactivated and RNAase is released from the RNAase-inhibitor complex during metamorphosis.

Interaction between membrane functions and protein synthesis in reticulocytes. Isolation of RNase M, a membrane component inhibiting protein synthesis through specific endonucleolytic activity

An inhibitor of protein synthesis has been isolated from reticulocyte membranes by solubilization with Triton X-100; it has been purified using heat treatment, filtration on Amicon filters, DEAE-cellulose ion-exchange chromatography and Sephadex G-75 gel chromatography. A final purification of 120-fold was achieved. The purified inhibitor was found to be 95% homogenous when run on a dodecylsulfate/polyacrylamide gel system. Three independent methods were used to estimate the molecular weight of the purified inhibitor: Sephadex G-75 gel chromatography, dodecylsulfate/polyacrylamide gel electrophoresis and sucrose gradient all confirmed that the purified inhibitor was a small molecule with a sedimentation coefficient of 0.7 S and a molecular weight ranging between 5000 and 8000. The purified inhibitor was shown to possess a specific endonucleolytic activity, degrading the 28-S species of ribosomal RNA to species sedimenting between 10 and 14 S. Due to its membrane localisation the name RNase M is proposed. The purified inhibitor's endonucleolytic activity was characterized with regard to its kinetics, concentration dependence, pH optimum and its requirements for divalent cations. Kinetics showed that RNase M retained its specificity after 60 min of incubation with the RNA substrate. Specificity was also demonstrated by incubating the polysomal RNA with high concentrations of purified enzyme. The pH optimum was found to be between pH 6 and pH 7, and the enzyme did not require divalent cations for its activity. Pancreatic RNase B used at a similar protein synthesis inhibitory concentration as the RNase M caused a complete breakdown of ribosomal RNA to oligonucleotides and mononucleotides. The possible biological significance of the purified inhibitor in regulating protein synthesis in the maturing reticulocyte is discussed.