TABLE 1.

Purification of complementing activity from baboon kidney extract^a

Step	Total protein (mg)	Total activityb (U)	Sp act (U/mg)	Purification (fold)	Recovery (%)
1. WCE	952	15,001	15.7	1	100
2. 15 to 30% AMS	115	12,340	107	6.8	82
3. Sephacryl S300	54	9,600	178	11.3	64
4. RNA affinity	0.00025c	550	2,200,000	140,127	3.6

^aComplementing activity was purified from whole-cell extracts (WCE) obtained from 20 g of baboon kidney by precipitation with 15 to 30% ammonium sulfate (AMS) and gel filtration on Sephacryl S300. For RNA affinity chromatography, proteins were precleared with a mutant apo-B RNA column. The unbound fraction was incubated with the wild-type RNA affinity column, and the bound proteins were eluted with 0.5 M NaCl. 

^bOne unit is defined as the amount of complementing activity that edits 1 fmol of apo-B RNA/h in the presence of recombinant apobec-1. 

^cBecause of the low yield, the total protein in this fraction was estimated by silver staining in comparison with known standards.