passages.id: split_4_test_3105_passage
passages.type: progene_text
passages.text: We find that although the family forms part of a larger superfamily of deaminases distributed throughout the biological world , the AID / APOBEC family itself is restricted to vertebrates with homologs of AID ( a DNA deaminase that triggers antibody gene diversification ) and of APOBEC2 ( unknown function ) identifiable in sequence databases from bony fish , birds , amphibians , and mammals .