The first-step transfer-DNA injection-stop signal of bacteriophage T5.

Bacteriophage T5 is different from most phages in that its DNA is injected in two steps during infection. The region containing the injection stop signal (iss) has been cloned and sequenced and found to contain numerous large repeats and inverted repeats which may be part of the iss. The most impressive of these are the 31-bp repeat units (rb) which are present three times in 99 bp. The rb repeats, themselves, contain inverted repeats so that mutually exclusive stem-and-loop structures may potentially form, not only within the repeats, but also between them. Another pair of repeats (21 bp each) contains two sequences resembling DnaA protein-binding sites. The region sequenced also contains one of the T5 site-specific strand interruptions and this was found to lie at the base of a perfect 9-bp palindrome.