Fig. 8. Growing wild-type cells secrete a 150 kDa factor that represses cell proliferation, and aprA^- cells do not accumulate this factor. Conditioned growth media from the indicated cell types were fractionated on the Superose gel filtration column used for Fig. 1. Indicated fractions (5 µl), as well as 5 µl of the column buffer (Buffer) were added to wild-type cells, and the cells were counted 24 hours later. Values are means±s.e.m. from three independent assays. The difference between the counts for fraction 29 of the exudates from wild type and aprA^- is significant (P<0.025; t-test).