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* Ribonuclease T2 family histidine active sites *
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The fungal ribonucleases T2 from Aspergillus oryzae, M from Aspergillus saitoi
and Rh from Rhizopeus niveus  are structurally  and functionally related 30 Kd
glycoproteins [1] that cleave the 3'-5' internucleotide  linkage  of RNA via a
nucleotide 2',3'-cyclic phosphate intermediates (EC 3.1.27.1).

A number of other RNAses  have  been found to be evolutionary related to these
fungal enzymes:

 - Self-incompatibility [2]  in  flowering  plants  is  often  controlled by a
   single gene   (S-gene)   that  has  several  alleles.  This  gene  prevents
   fertilization by  self-pollen  or  by  pollen  bearing either of the two S-
   alleles expressed  in the style. The self-incompatibility glycoprotein from
   several higher  plants of the solanaceae family has  been shown [2,3] to be
   a ribonuclease.
 - Phosphate-starvation  induced  RNAses  LE and LX from tomato [4]. These two
   enzymes are probably involved in a phosphate-starvation rescue system.
 - Escherichia coli periplasmic RNAse I (EC 3.1.27.6) (gene rna) [5].

Two histidines residues have been shown [6,7]  to be involved in the catalytic
mechanism of RNase T2 and Rh.  These  residues  and the region around them are
highly conserved in all  the sequence described above.  We  have developed two
signature patterns, one  for  each  of  the two  active-site  histidines.  The
second pattern  also  contains  a cysteine which is  known to be involved in a
disulfide bond.

-Consensus pattern: [FYWL]-x-[LIVM]-H-G-L-W-P
                    [H is an active site residue]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in SWISS-PROT: NONE.

-Consensus pattern: [LIVMF]-x(2)-[HDY]-[EQ]-[FYW]-x-[KR]-H-G-x-C
                    [H is an active site residue]
                    [C is involved in a disulfide bond]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in SWISS-PROT: genome   polyproteins  from  Bovine
 viral diarrhea virus and Hog cholera virus.  It seems that these pestiviruses
 polyproteins include a RNAse T2-like domain [8].

-Last update: October 1993 / Patterns and text revised.

[ 1] Watanabe H., Naitoh A., Suyama Y., Inokuchi N., Shimada H., Koyama T.,
     Ohgi K., Irie M.
     J. Biochem. 108:303-310(1990).
[ 2] Haring V., Gray J.E., McClure B.A., Anderson M.A., Clarke A.E.
     Science 250:937-941(1990).
[ 3] McClure B.A., Haring V., Ebert P.R., Anderson M.A., Simpson R.J.,
     Sakiyama F., Clarke A.E.
     Nature 342:95957(1989).
[ 4] Loeffler A., Glund K., Irie M.
     Eur. J. Biochem. 214:627-633(1993).
[ 5] Meador J. III, Kennell D.
     Gene 95:1-7(1990).
[ 6] Kawata Y., Sakiyama F., Hayashi F., Kyogoku Y.
     Eur. J. Biochem. 187:255-262(1990).
[ 7] Kurihara H., Mitsui Y., Ohgi K., Irie M., Mizuno H., Nakamura K.T.
     FEBS Lett. 306:189-192(1992).
[ 8] Bairoch A.
     Unpublished observations (1993).