Amino acid sequence and characterization of a rice bran ribonuclease

A base-nonspecific and acid ribonuclease (RNase Os) belonging to the RNase T2 family was purified from rice bran to a homogeneous state by SDS-PAGE, T he primary structure of RNase Os was determined by protein chemistry and mo lecular cloning. The RNase Os was a simple protein and consisted of 205 ami no acid residues. Its molecular weight was 22578 and its amino acid sequenc e showed that it was most similar to barley RNase among the known RNase T2 family enzymes having 157 amino acid residues identical with barley RNase, However, its N-terminus was blocked by a gamma -pyroglutamyl residue. The o ptimal pH of RNase Os was around 5.5, The base preference at the B1 and B2 site of RNase Os was estimated from the rates of hydrolysis of 16 dinucleos ide phosphates, to be guanine as the case of RNase LE from tomato. RNase Os was successfully expressed from yeast cells using the E.coli/yeast express ion vector pYE-RNAP.