Bacteriophage T4-infected E. coli present an understandable system in which regulatory loops (involving sequential classes of global transcription, gene-specific translational repression, and, perhaps, regulated mRNA splicing) conspire to utilize most of the infected cells' resources to yield new viruses. T4 effectively redirects cellular metabolism away from ribosome biosynthesis toward virus production; a major redirection is the substitution of viral DNA synthesis for rRNA synthesis. This study of the T4 replisome and the regulation of the flow of substrates into DNA and protein is aimed at understanding growth control and optimal resource management. T4-encoded replisome participants are often bifunctional. Gene 43 encodes the DNA polymerase of T4, and represses its own translation. Gene 32 encodes the major single-stranded DNA binding protein of T4, represses its own translation when no single- stranded DNA is available, and participates in the important coordination between DNA replication and late T4 transcription. The regA protein represses and/or activates translation of perhaps twenty T4 early mRNAs and probably has a primary function in the replisome. MotA activates the middle transcripts (which encode numerous replisome proteins), represses some early transcripts, and has a direct role in the replisome, probably as a DNA binding protein. A study of these four proteins will provide textures to the feedback loops that regulate the amount of replication (and late transcription and translation of phage structural genes) in response to environmental opportunities. The regulation of mRNA self-splicing will also be studied, since the mRNAs containing type I introns point toward management of reducing power. T4 origins of replication will be studied through the identification of sequences that function early and specifically to establish replication forks. Establishment of replication forks is regulated by the bifunctional proteins of the replisome and DNA synthesis is regulated at the level of initiation. Replication regulation is tied to the cell's energy charge and level of reducing power. Small molecule effectors of T4 measure energy change and reducing power in order to set macromolecular biosynthesis at appropriate levels. Relationships between small molecules and macromolecule synthesis will be established.
