We purified the proteins of all four SVs and seven haplotypes (Hap I–VII) of A3H in large quantity from E. coli expression system.

We showed that three of the four SVs and three haplotypes (hap II, V, VII) all have very high deamination activity on C, with hap I showing ~ 1/10 of the activities of other three haplotypes.

We revealed that for A3H hap II, the deamination activity on mC is almost as efficient as on C for the DNA substrates containing -mCpG- or -CpG- motif.

We showed that the deaminase activity of different A3H variants correlates well with their reported anti-HIV activity, indicating the importance of deaminase activity for HIV restriction.