Q Protein and Late Protein Synthesis
The final genes in the early operons are the int and xis genes on the left and the Q gene on the right. The int and xis genes are important in the lysogenization process and are discussed in a later chapter. The Q protein functions as an antiterminator of a promoter located immedi-ately to its right. Without Q protein, polymerase initiates at this pro-moter and terminates 190 bases later (Fig. 14.9). When Q protein is
Figure 14.9 Action of Q protein in preventing premature termination attRâ€™.
present, this termination is abolished, and transcription proceeds across the S and R genes, across the ligated sticky ends, and into the remaining late genes. These code for the head and tail structures of the phage. Since transcription of the late genes occurs at a time when about 40 copies of the DNA exist in the cell, large quantities of late mRNA are synthesized.