Cloning and expression of a chloramphenicol acetyltransferase gene in cytosine-substituted T4 bacteriophage

Transactivation of a plasmid-borne bacteriophage T4 late gene

We examined how a plasmid-borne T4 late gene is activated by infecting T4 phage (transactivation). A gene fusion system was developed where expression of a late gene promoter fused to the lacZ gene may easily be followed by measuring beta-galactosidase activity. Considerable transactivation can occur, provided that the infecting phage contains a mutation which abolishes the denB-encoded endonuclease, and that the gene 46-encoded exonuclease is functional. The level of transactivation was correlated with the formation of high molecular weight DNA composed of tandem repeats of plasmid DNA. The formation of these molecules and subsequent transactivation depended on DNA replication and homology between phage and plasmid DNAs. Also the capacity of bacteriophage T4, grown on cells containing a plasmid-borne T4 gene, to transduce the plasmid provided indirect evidence of the formation of these tandem-repeat molecules. A good correlation was established between the ability to transduce and the presence of sequence homology between the phage and the plasmid. However, the requirement for phage/plasmid homology is no longer prerequisite if transcription from the plasmid is permitted by introducing an alc mutation into the infecting phage, presumably because this allows DNA replication to start through RNA priming.

Activation and quantitative estimation of bacteriophage T4 late regulatory signal in cis- and transconditions

Activation of the bacteriophage T4 late gene 22 carried on the phage genome (ciscondition) or borne on a plasmid (transcondition) was quantitatively analyzed after phage infection using a lacZ reporter gene. Transcription from the late promoter was activated postreplicatively by concomitantly infecting T4 phage. A truncated T4-lacZ gene including only 15 bp of sequence upstream of the late promoter consensus of gene 22 TATAAATA, was fully activated in the ciscondition but induced to a reduced extent in the transcondition. A possible mechanism for trans-activation is discussed.

An efficient method for constructing a chimeric bacteriophage T4 to estimate the regulatory signals

A system for the quantitative estimation of T4 regulatory signals in bacteriophage T4 was developed. We constructed a transmitter-reporter [corrected] plasmid vector, pCV22, which is able not only to fuse transcriptional and translational signals to the coding region of lacZ gene (reporter) but also to transmit the fused gene into T4 phage genome (transmitter). The regulatory signals of T4 phage genes fused with the reporter gene was transmitted efficiently into T4 phage (T4dC-lac phage; a receiver phage) by a replacement type of recombination in the uvsY gene region. This type of chimeric phage was demonstrated to be able to quantitatively estimate the late regulatory signal of T4 phage in vivo.