| pubmed-article:8464062 | pubmed:abstractText | cosB is the binding site on lambda DNA for terminase, the phage DNA packaging protein. cosB contains three binding sites for gpNu1, the small subunit of terminase, and a site for integration host factor (IHF). IHF plays an accessory role in lambda DNA packaging, and IHF stimulates the burst size of lambda several-fold, presumably by assisting the interaction of terminase with cosB. The present work includes a study of the effect on lambda development of a mutation, called I1A-, which consists of three adjacent base-pair changes in the IHF binding site. The I1A- mutation was found to abolish IHF stimulation of the lambda burst size, indicating that IHF is unable to bind to the mutant I1A site. A second mutation, called I1B- and also consisting of three adjacent base-pair changes, is a mutation that reduces an intrinsic bend found in cosB. lambda I1B- was more dependent on IHF than lambda+, raising the possibility that the intrinsic bend in cosB plays a role in cos function for lambda+ under the IHF- conditions. In vitro DNA packaging experiments established that the I1 mutations affect DNA packaging per se. A series of Nu1 mutations that create terminases able to suppress a variety of cosB defects were found to suppress the defects of the I1A- and I1B- mutations under IHF- conditions. | lld:pubmed |
