Abstract
With the use of a precursor to Escherichia coli tRNA-Tyr as a substrate, we have detected and partially purified a novel endoribonuclease from the cytoplasm of human KB tissue culture cells. This activity, which we have called RNase NU, cleaves the tRNA precursor at two sites in that part of the molecule which is not included in the mature tRNA sequence and which is normally degraded in vivo. In keeping with this observation, we have found that, of a variety of substrates tested, only those which are unstable in vivo are attacked by RNase NU. RNase NU can be purified from the 0.2 M NH4Cl wash of ribosomes followed by ammonium sulfate fractionation and DEAE-Sephadex chromatography. RNase NU cleaves RNA to create 3'-phosphate-terminated oligonucleotides. It has a pH optimum near 8.0, requires either a monovalent cation (NH4+ is most efficient) or Ca-2+ for optimal activity, and is inhibited by 0.1 M PO4-3-. In the course of purifying RNase NU we have detected and studied the intracellular distribution of other ribonuclease activities in human KB cells.
Highlights
With the use of a precursor to Escherichia coli tRNATY’ as a substrate, we have detected and partially purified a novel endoribonuclease from the cytoplasm of human KB tissue culture cells
RNase NU can be purified from the 0.2 M NH&l wash of ribosomes followed by ammonium sulfate fractionation and DEAE-Sephadex chromatography
With the use of a precursor to an E. coli tRNA Tyr species (I, 17) as substrate, we have examined extracts of human KB tissue culture cells for ribonuclease activity
Summary
With the use of a precursor to Escherichia coli tRNATY’ as a substrate, we have detected and partially purified a novel endoribonuclease from the cytoplasm of human KB tissue culture cells. This activity, which we have called RNase. In initiating studies of RNA metabolism in new cell types, we have decided to use a radiochemically homogeneous, natural substrate as a sensitive probe for specific endoribonucleases. This approach has proved to be fruitful. In this report we describe the partial purification and properties of an enzymatic activity which appears to cleave only unstable RNAs such as the tRNA precursor or messenger RNAs, but not stable RNAs, such as mature tRNA, 5 S RNA, or ribosomal RNA
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
