Ribonucleases of diverse specificities in rabbit brain nuclei

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Abstract
A salt extract of rabbit brain nuclei contains three endoribonucleases, designated RNases Y, A and R, which produce acid‐soluble products when incubated at near‐neutral pH in the absence of metal ions. RNases Y and A yield products with the monoesterified phosphate at the 3′ position, through 2′,3′‐(cyclic)phosphate intermediates. Oligonucleotides terminating with a 2′,3′‐(cyclic)phosphate are the end‐products of the action of RNase R. Double‐stranded substrates are highly resistant to the action of all enzymes. On the basis of limited hydrolysis of end‐labelled 5S RNA, the three enzymes differ in their preference for the susceptible phosphodiester bond. Thus, RNase Y hydrolyses preferentially the YpN bond, RNase A the ApN bond and RNase R the RpU bond where R is guanosine in most cases. The advantages and disadvantages of using homopolyribonucleotides and dephosphorylated dinucleotides and trinucleotides in determining various aspects of the specificity of RNases are discussed.