We have performed a new screen for T4 mutants (comC) that overcome the phage growth restriction caused by the Escherichia coli rho/tabC mutants. We show that one such mutant (comCJ) identifies a different gene from that identified by canonical comC mutants. We compare the regulation of T4 prereplicative transcription in a rho/tabC mutant infected by T4 wild-type, by a canonical comC mutant (comC alpha 55.6) and by comCJ. The transcription rates of the two prereplicative genes 39 and 43 is depressed in a T4 wild-type infected tabC host mutant. When comC alpha 55.6 and/or comCJ single and double mutants are the infecting phages, transcription of genes 39 and 43 is resumed to different extents; in particular, in the double mutant infections there appears to be a synergistic effect on transcription. Furthermore, we find that the comC alpha 55.6 phage mutant affects the transcription rate of the gene rIIA in a wild-type host.