Studies on extracellular ribonucleases of Ustilago sphaerogena. Characterization of substrate specificity with special reference to purine-specific ribonucleases.
1. Ribonuclease U(1) splits only the phosphodiester bonds of guanosine 3'-phosphates in RNA. It may be regarded as a guanyloribonuclease [ribonucleate (guanine nucleotide)-2'-transferase (cyclizing), EC 2.7.7.26] similar to ribonuclease T(1) (Egami, Takahashi & Uchida, 1964). It seems to be identical with the extracellular ribonuclease described by Glitz & Dekker (1963, 1964a,b). 2. Ribonucleases U(2) and U(3) are novel enzymes with a strict specificity. They split the internucleotide bonds between purine 3'-nucleotides and 5'-hydroxy groups of adjacent nucleotides in RNA with the intermediary formation of purine nucleoside 2',3'-(cyclic)-phosphates, which are slowly hydrolysed to purine 3'-nucleotides. So they may be classified as ;puryloribonucleases [ribonucleate (purine nucleotide)-2'-transferase (cyclizing)]'. Double-stranded RNA is scarcely split by ribonucleases U(2) and U(3). 3. Ribonuclease U(4) has no absolute base specificity, and produces the mononucleotides 3'-adenylate, 3'-guanylate, 3'-cytidylate and 3'-uridylate from RNA.
D000227:Adenine Nucleotides / Q000378:metabolism*; D001487:Basidiomycota / Q000201:enzymology*; D002854:Chromatography, Paper; D006150:Guanine Nucleotides / Q000378:metabolism*; D012313:RNA / Q000378:metabolism*; D012367:RNA, Viral / Q000378:metabolism*; D012260:Ribonucleases / Q000378:metabolism*; D013053:Spectrophotometry
D000227:Adenine Nucleotides; D006150:Guanine Nucleotides; D012367:RNA, Viral; D012313:RNA; D012260:Ribonucleases