Abstract
Escherichia coli bacteriophage T5 differs from most phages in that it injects its genome in two steps: First Step Transfer, FST, corresponding to leftmost 7.9% of the genome and Second Step Transfer, SST, corresponding to the remainder of the genome. Expression of genes A1 and A2 is required for SST. DNA injection stops at a site known as the injection stop signal (iss) which is a cis acting site located in the untranslated region of the Left Terminal Repeat (LTR). The iss region is extremely complicated with many repeats, inverted repeats and palindromes. This report compares the iss regions of 21 T5 related phages and shows that all have a common conserved structure including a series of 8 DnaA boxes arranged in a highly specific manner; reminiscent of the origin of replication (oriC) of the host. DnaA protein, which binds DnaA boxes is a mostly membrane bound, leading to the suggestion that injection stops at iss due to binding to DnaA protein at the membrane. A new model of the mechanism of T5 injection stop and SST injection re-start is suggested.