DNA Packaging Specificity in the λ-like Phages: Gifsy-1

DNA viruses recognize viral DNA and package it into virions. Specific recognition is needed to distinguish viral DNA from host cell DNA. The λ-like phages are interesting and good models to examine viral DNA packaging, and the Escherichia coli phage λ has been extensively studied. Gifsy-1 is a Salmonella phage largely genetically isolated from coliphage λ due to their different host ranges. In this present work, Gifsy-1’s DNA packaging specificity was studied using a Gifsy-1-λ hybrid phage with the Gifsy-1 recognition elements – the TerS protein’s winged helix-turn-helix DNA binding motif and cosB , the TerS binding site. In vivo packaging studies showed Gifsy-1 packages λ DNA at ⁓50% and λ packages Gifsy-1 DNA at ⁓ 30% efficiency, and thus share the same DNA packaging specificity. N15 is a third phage that shares phage λ’s packaging specificity. Here N15 is shown to package Gifsy-1 DNA. Phage 21 fails to package λ and Gifsy-1 DNAs; the efficiencies are 0.01% and 1%, resp. A known incompatibility between the 21 helix-turn-helix motif and cosB is also proposed to account for the inability of 21 to package Gifsy-1 DNA.