Heat Induced Capsid Disassembly and DNA Release of Bacteriophage λ

Successive structural changes of bacteriophage [Image: see text] upon heating were characterized with quantitative experimental methods. In the commonly used Tris-Mg buffer, differential scanning calorimetry measurements first established that the protein capsid of [Image: see text] phage melts at 87°C and its genomic DNA melts at 91°C. Interestingly, prior to the capsid melting, [Image: see text]DNA was found to escape out of the capsid and subject to DNase digestion above [Image: see text]68°C, as concluded from light scattering, UV absorption, and electron microscopy studies. Further investigations indicated distinct temperature-dependent behaviors of the three phage proteins. Around 68°C, disruption of the tail first occurs and leads to the escape of [Image: see text] DNA; above the capsid melting temperature of 87°C, the auxiliary protein gpD of the phage head remains soluble in solution and resists centrifugal sedimentation, whereas the major capsid protein gpE is easily precipitated and likely exists as aggregates.