Events in lambda injection between phage adsorption and DNA entry

Injection kinetics indicate that, in the time period from irreversible adsorption through stable uptake of λ DNA, several reactions must occur in or between the phage and the bacterium. The events are grouped in three steps: lag, triggering, and uptake. The results further suggest that an exchange of information occurs between the distal and the proximal ends of the phage tail. The triggering of DNA injection from λ preadsorbed to Escherichia coli is essentially immediate at 37° but occurs only after a lag of 6 min at 25° or 10 min at 23°. At 15°, injection does not occur. When phage-cell complexes are incubated at 37° in 10 m M putrescine-10 −5 M Mg 2+, the lag functions are completed but injection is blocked. After resuspension in normal buffer (10 m M Mg 2+, 10 m M phosphate, pH 7.1), DNA injection is triggered without a lag, even at 12.5°. It still does not occur at 4°. Events during the lag involve more than a simple interaction between the tail tip and the outer membrane of the bacterial cell wall. When tails alone are attached to cells, incubated at 37 or at 4°, and then joined with heads in vitro at 4°, the resulting phage particles inject at 25° with the same kinetics, including a lag, regardless of whether the tail-bacterial complexes initially were incubated at 37 or at 4°. When phage-cell complexes in which the λ DNA is 3H-labeled are treated with CHCl 3 and then incubated at 37°, 90% of the labeled DNA is ejected from the phage but it is found in the medium rather than inside the host cell. If cells are exposed to chloroform prior to phage attachment of after the phage-cell complex has completed the lag reaction, the pattern of triggering and of uptake is very different. This reflects, in another way, the existence of several different possible states during injection.