anabolic enzyme-->catabolic enzyme

[John J Weiland]

Has anyone ever seen description of an anabolic enzyme (polymerase, 
acetylase, kinase, etc) converted into a catabolic enzyme with the 
specificity that is the reverse of the original anabolic one?  For 
example, can RNA polymerase be converted to a ribonuclease by mutation of 
the RNA polymerase gene, or can a kinase be converted to a phosphatase in 
a similar manner?  Is there any example of this occuring naturally?  
Thus, have any DNA endonucleases been sequenced and found to be similar 
in structure to DNA ligase, etc?  Any references would be of help!  Thanks.

John Weiland