0 Evilevitch, A Gober, JW Phillips, M Knobler, CM Gelbart, WM 2005 BIOPHYSICAL JOURNAL 88 751-756 JAN BACTERIOPHAGE-LAMBDA, SEDIMENTATION, EXPRESSION, FORCES, PHAGE The effect of external osmotic pressure on the extent of DNA ejection from bacteriophage-lambda was recently investigated (Evilevitch et al., 2003). The total length of DNA ejected was measured via the 260-nm absorption by free nucleotides, after opening of the capsids in the presence of varying amounts of polyethylene glycol 8000 and DNase I. As a function of osmolyte concentration, this absorption was shown to decrease progressively, ultimately vanishing completely for a sufficiently high external osmotic pressure. In this work we report the results of both sedimentation and gel analysis of the length of DNA remaining inside the capsids, as a function of osmolyte concentration. It is confirmed in this way that the progressive inhibition of DNA ejection corresponds to partial ejection from all of the capsids. http://dx.doi.org/10.1529/biophysj.104.045088