Figure 3.

Ultrafiltration experiments show that the QSF is a large secreted molecule. (a) Principle of the ultrafiltration (example based on CM) and blend of the various fractions. (b) QSF activity for different test media. Both FM and CM have been separated in a filtrate and a supernatant (respectively, denoted by an ‘f’ and an ‘s’ subscript) using a 3 kDa cut-off, then various combinations of these fractions have been tested for QSF activity. n = 2 (FM_s:FM, CM_s:FM) and 3 for all other conditions. The symbols (and colours online) above the bars refer the corresponding curves in (c). (c) QSF activity in self- and cross-mixes of filtrate and supernatant for various pore sizes: CM_s:CM_f (triangles), CM_s:FM_f (squares), FM_s:CM_f (circles). The QSF activity switches from CM_s to CM_f at M ≃ 50 kDa (MWCO given for globular molecules; the corresponding molecular weight for a linear molecule would be 10 kDa). (d) QSF activity in media subjected to treatment with phenol–chloroform, proteinase K, cation- and anion-exchange resins. Control media (Ctrl) and treated media (Test). See Material and methods section for more details. All plots, mean ± s.d. from n ≥ 3 experiments. (Online version in colour.)