Pancreatic ribonucleases (EC 3.1.27.5) are pyrimidine-specific endonucleases present in high quantity in the pancreas of a number of mammalian taxa and of a few reptiles [1,2]. As shown in the following schematic representation of the sequence of pancreatic RNases there are four conserved disulfide bonds and three amino acid residues involved in the catalytic activity.

                        +---------------------------+
                        |        +------------------|------+
                        |        |                  |      |
     xxxxx#xxxxxxCxxxxxxC#xxxxxxxCxxCxxxCxxxxxCxxxxxCxxxxxxCxxx#xxx
                 |      ****        |   |     |
                 |                  +---+     |
                 +----------------------------+

'C': conserved cysteine involved in a disulfide bond.
'#': active site residue.
'*': position of the pattern.

A number of other proteins belongs to the pancreatic RNAse family and these are listed below.

• Bovine seminal vesicle and bovine brain ribonucleases.
• The kidney non-secretory ribonucleases (also known as eosinophil-derived neurotoxin (EDN) [3]).
• Liver-type ribonucleases [4].
• Angiogenin, which induces vascularization of normal and malignant tissues. It abolishes protein synthesis by specifically hydrolyzing cellular tRNAs.
• Eosinophil cationic protein (ECP) [5], a cytotoxin and helminthotoxin with ribonuclease activity.
• Frog liver ribonuclease and frog sialic acid-binding lectin [6].

The signature pattern we developed for these proteins includes five conserved residues: a cysteine involved in a disulfide bond, a lysine involved in the catalytic activity and three other residues important for substrate binding.