This domain is an ADP-ribose binding module. It is found in a number of otherwise unrelated proteins. It is found at the C-terminus of the macro-H2A histone protein. This domain is found in the non-structural proteins of several types of ssRNA viruses such as NSP3 from alphaviruses. This domain is also found on its own in a family of proteins from bacteria, archaebacteria and eukaryotes.