RIBONUCLEASES FROM RAT AND BOVINE LIVER - PURIFICATION, SPECIFICITY AND STRUCTURAL CHARACTERIZATION

The presence of four members of the pyrimidine-specific ribonuclease s uperfamily was demonstrated in rat liver. Three of them (RL1, RL2 and RL3) were purified and showed ribonuclease activity at pH 7.5 with yea st RNA as substrate. RL1 is identical to rat pancreatic ribonuclease ( ribonuclease 1). N-terminal sequence analysis showed the presence of t he native protein and several N-terminally degraded components. RL2 an d RL3 were N-terminally blocked proteins. After acidic cleavage or CNB r digestion, several parts of their sequences were determined. RL2 has high sequence similarity with neurotoxin-type ribonucleases (ribonucl eases 2, 3 and 6). The amino acid sequence of rat liver-type ribonucle ase (ribonuclease 4) was determined from a liver cDNA library. It diff ers at about 20% of the amino acid positions from other mammalian live r-type ribonucleases. The sequence of a peptide of RL3 was identical t o that derived from the cDNA sequence of the liver-type ribonuclease, A contaminant of the RL3 fraction had a high sequence similarity with mouse and other mammalian angiogenins. Bovine, porcine and rat liver-t ype ribonucleases showed a strong preference for poly(U) over poly(C). This preference is a unique property of the liver-type enzymes of the ribonuclease superfamily. (C) 1998 Elsevier Science B.V.