The sequence and mom-transactivation function of the C gene of bacteriophage Mu.

The mom gene of bacteriophage Mu encodes a DNA modification function. The gene is regulated on the transcriptional level by Dam-specific methylation and a trans-acting Mu function, and on a post-transcriptional level by the product of gene com. The gene encoding the transactivator has been cloned and mapped. By complementation analysis the activation function (also designated Dad) was shown to be the product of gene C. Transactivation of the mom promoter was shown in the following assay: the mom promoter and N-terminal part of com were fused in frame to lacZ. Cells containing such fusion plasmids were infected with M13 clones expressing C in the presence of IPTG and XGal. Successful transactivation results in the formation of blue plaques. Moreover, we have determined the sequence of gene C and found that it has a coding capacity of 140 amino acids. The promoter for C (pc) is likely to be located at least 0.5 kb upstream from the gene. A transcription terminator is found directly downstream from the C-coding region.