Repetitive DNA Replication of the Incomplete Genomes of Phage T4 Petite Particles

The genomes of petite T4 phage particles presumably cannot circularize because they are deficient for a significant terminal segment and hence not terminally redundant like normal T4 genomes. Combined density- and32P-labeling shows that the majority of such deficient DNA molecules can nevertheless replicate their entire length. Furthermore, the density-shift technique shows that replicated parental strands can exchange their partners for new light strands, indicating that noncircularized T4 DNA molecules replicate repeatedly. When taken together with previously published data, these results indicate that T4 replication is bidirectional from multiple, genetically fixed points of origin. Rolling circle models can, therefore, not be considered as an essential mechanism for the early rounds of T4 replication.