Abstract
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 λ is
also proposed to account for the inability of 21 to package Gifsy-1 DNA.