The ribonuclease inhibitor (RI) is a cytosolic protein and a potent inhibitor of bovine pancreatic ribonuclease (RNase A). Amphibian homologues and variants of RNase A that evade RI are cytotoxic. Here, we employ RNA interference along with amphibian and mammalian ribonucleases to demonstrate that RI protects cells against exogenous ribonucleases. These data indicate an imperative for the molec...

Lactose has been coupled to the lysine residues of the cross-linked dimer of bovine pancreatic ribonuclease A by reductive amination with cyanoborohydride. Derivatives of ribonuclease dimer that contained up to 10 Nepsilon-1-(1-deoxylactitolyl)-lysine residues per molecule had greater than 75% of the enzymic activity of the unmodified enzyme toward yeast RNA. Upon intravenous injection of the 1...

The protein stabilizing effects of the small molecule osmolyte, trimethylamine N-oxide, against chemical denaturant was investigated by NMR spin-relaxation measurements and model-free analysis. In the presence of 0.7 M guanidine hydrochloride increased picosecond-nanosecond dynamics are observed in the protein ribonuclease A. These increased fluctuations occur throughout the protein, but the mo...

Human placental ribonuclease inhibitor (PRI) abolishes both the ribonucleolytic activity of angiogenin toward 28S and 18S rRNA and its angiogenic activity on the chicken embryo chorioallantoic membrane. Treatment of the angiogenin-PRI complex with p-hydroxymercuribenzoate releases enzymatically active angiogenin. Assays measuring competition between angiogenin and bovine pancreatic ribonuclease...

The proteolysis of bovine pancreatic ribonuclease by subtilisin has been shown to involve the formation of an enzymically active intermediate which is further degraded to inactive products (1, 2). This paper describes the preparation of the modified active ribonuclease, RNase (S)l and its fractionation into two components, a peptide (S-peptide) and a protein (S-protein). Neither S-peptide nor S...

Ribonuclease activity in cell-free thymus homogenates was elevated for five strains of mice genetically predisposed toward leukemia or reticulum cell neoplasms (AKR, C58, PL, RF, and SJL). Such increased activity was directed against polyuridylic acid and was observed in 8-wk old mice, well before the onset of neoplastic transformation. Similarly, white blood cell ribonuclease activity was elev...

Wild-type ribonuclease A and five mutants thereof have been expressed in Escherichia coli as fusion proteins by using a T7 expression system. The five mutants are C[65-72]S, C[40-95]S, C[58-110]S, C[26-84]S, and K41G. The expressed fusion protein formed inclusion bodies which were then cleaved by factor Xa. The cleaved ribonuclease A was isolated as unfolded (sulfonated), soluble protein which ...

Fibrillarin is one of the most important nucleolar proteins that have been shown as essential for life. Fibrillarin localizes primarily at the periphery between fibrillar center and dense fibrillar component as well as in Cajal bodies. In most plants there are at least two different genes for fibrillarin. In Arabidopsis thaliana both genes show high level of expression in transcriptionally acti...

Spectrophotometric titration studies and ultraviolet difference spectra are two techniques which have been used in recent years for determining what role, if any, the tyrosine residues in a protein play in maintaining the secondary and tertiary structure of proteins. Crammer and Neuberger (2) utilized a spectrophotometric procedure to investigate the ionization of phenolic groups in ovalbumin a...