Self-Help Fibronectin Assembly Figure 3. Identification of the fraction of ‘‘fingerless’’ fibronectin that supports exogenous fibronectin assembly by fibronectin-null cells as an adherent substrate. (A) ‘‘Fingerless’’ fibronectin was separated on a monoQ anionic exchange column. Three major peaks, 1, 2, and 3, were separated by a concentration gradient of NaCl. The likely modular compositions of fibronectin fragments in these peaks based on size and presence of epitopes for monoclonal antibodies are diagrammed in Fig. 1A and discussed in the text. (B) Supportive activity of the separated ‘‘fingerless’’ fibronectin proteins. After 2 hr incubation at 37uC of fibronectin-null cells on cover slips coated with peak 1, 2, or 3 at 3 mg/ml, 9 mg/ml Rx-fibronectin were added to culture medium, and cells were incubated for an additional 2 hr. Cells were assessed by fluorescence microscopy as PLoS ONE | www.plosone.org 5 January 2009 | Volume 4 | Issue 1 | e4113