PRIMARY STRUCTURE OF A SQUID ACID AND BASE NONSPECIFIC RIBONUCLEASE

Squid (Todarodes pacificus) liver RNase (RNase Tp) was purified. RNase Tp was a base non-specific and acid RNase. Upon hydrolysis of RNA, RN ase Tp released four mononucleotides in the order of G>A>U>C. RNase Tp consisted of two peptides with 198 and 23 amino acid residues. The am ino acid sequences of these peptides were analyzed. The large peptide had two unique segments containing most of the active site amino acid residues of RNase T2 family enzymes. From the comparison of the sequen ce of short peptide with the sequences of the other RNase belonging to RNase T2 family RNases, it was found that the amino acid sequence of the short peptide was very similar to that of the C-terminal portion o f RNases of the RNase T2 family. Thus, we concluded that the short pep tide was a C-terminal part of RNase Tp. The molecular mass of the prot ein moiety of RNase Tp was 25,582 daltons. The amino acid sequence of RNase Tp most resembles that of oyster RNase (91 amino acid residues i dentical) in the RNase T2 family RNases. However, the N-terminal porti on of RNase Tp was unusually similar to those of plant RNases, rather than the other animal RNases.