Function of a viral genome packaging motor from bacteriophage T4 is insensitive to DNA sequence*

Many viruses employ motors during assembly to translocate DNA into capsids. Previous reports raise questions if motor function depends on DNA sequence: i) The phage T4 motor exhibits large velocity fluctuations and pauses and slips, ii) Evidence suggests that the phage phi29 motor contacts DNA bases, and iii) a “B-A scrunchworm” model predicts that “A-philic” sequences that transition more easily to A-form would alter function. Here, we use optical tweezers measurements to compare translocation of phage, plasmid, and synthetic A-philic, GC rich sequences by the T4 motor. We observed no significant differences in motor velocities, even with A-philic sequences predicted to show higher rate, no significant changes in motor pausing, and only modest changes in slipping. To more generally test sequence dependence, we conducted correlation analyses across pairs of events. No significant correlations in packaging rate, pausing, or slipping versus position were detected across repeated measurements with different DNA sequences. These studies suggest that the viral motor insensitive to DNA sequence and fluctuations in packaging velocity, pausing, and slipping are primarily stochastic temporal events.