The genome of virulent coliphage T5 contains about 30 sites which form stable complexes with E. coli RNA polymerase. Some of these sites bind RNA polymerase with high rates, others form extremely stable complexes as compared with promotors of other E. coli systems. The transcriptional activity of these promotors in vivo and in vitro reflects the rate of complex formation with RNA polymerase rather than the stability of the enzyme/promotor complex. The fastest, i.e. the most active promotors are found in the "early" region of gene expression followed by promotors of the "preearly" class. The few binding sites for the E. coli holoenzyme within the "late" region react more slowly with the enzyme.
Binding Sites Coliphages