The T4 mot protein functions as part of a pre-replicative DNA-protein complex.

Middle-mode RNA synthesis in T4-infected cells takes place before replication of phage DNA commences. What distinguishes it from early-mode RNA synthesis is that initiation of middle RNA depends on T4-coded proteins, in particular on the mot gene product. mot protein is localized in a DNA-protein complex which forms during the first few minutes of infection. All of the cell's mot protein is bound in this complex, and it continues to be bound long after the synthesis of mot protein has stopped. When we infect Escherichia coli with T4 carrying a temperature-sensitive mutation in the mot gene, we find a correlation between the physiology of this mot mutant and the amount of mot protein bound in the DNA-protein complex. Although there is some host RNA polymerase in the complex, mot protein does not seem to bind to this enzyme. Two other T4-coded proteins, of molecular weights 17,600 and 15,000, are also found in the pre-replicative DNA-protein complex. One of these, p17,600, is coded for by a 750-base pair region located between genes 39 and 56; p17,600 appears to be the recently described motB gene product. The other protein, p15,000, is not an RNA polymerase-binding protein; it is characterized by its strong binding to the DNA-protein complex.