Green fluorescent protein as a probe of rotational mobility within bacteriophage T4

Green fluorescent protein (GFP) was targeted into bacteriophage T4 heads and proheads as a probe of the internal environment. Targeting was accomplished with internal protein III (IPIII) fusion proteins or capsid targeting sequence (CTS)-tagged proteins, where CTS is the 10-amino acid residue CTS of IPIII. Recombinant phage T4[CTS black down triangle IPIII black down triangle GFP], T4[CTS black down triangle IPIII(T)GFP], and T4[CTS black down triangle GFP] packaged GFP fusion proteins and processed them at cleavage sites designated black down triangle. Steady-state and time-resolved fluorescence measurements suggest that packaged GFP is concentrated to a high density, that fusion protein IPIII(T)GFP occurs in a tightly clustered arrangement, and that the internal milieu of the phage head reduces rotational mobility of GFP. Phage, but not proheads, packaged with fusion protein IPIII(T)GFP gave an unexpectedly lower anisotropy than phage and proheads packaged with GFP, which suggests IPIII(T)GFP is bound to DNA in a manner that causes close associations between GFP molecules resulting in homotransfer between fluorophores within packaged phage. Targeting of reporter proteins into active virions is a promising approach for determining the structure of the condensed DNA, and properties of encapsidated viral enzymes. (C) Published by 2000 Elsevier Science B.V.