Figure 1.

Restriction maps of the cDNA copies of the genomic segments of Φ6, L, M, and S as well as diagrams of the chimeric constructions utilized in this study. The sequences are all embedded in plasmid pT7T319U, and the transcripts produced by T7 RNA polymerase have the correct base sequence at the 5′ ends. pLM1114 was prepared by ligating segment M cut at the PstI site to segment S cut at the BamHI site to form an MS chimera. Plasmid pLM1741 was constructed by cutting pLM659 with SacII and ligating to the HindIII site of segment M after blunting with T4 DNA polymerase. The segment M in this case had a type of Lacα inserted into the PstI site to adjust the size of the chimera to closely approximate the sum of segments S and M. Plasmid pLM1417 is a derivative of segment S in which the EcoRV site is ligated to a copy of the terminus of segment M to yield a segment S that is functional for packaging and replication but that contains no complete genes. Plasmid pLM1809 was constructed by ligating a cDNA copy of segment L cut at the SmaI site to pLM1741 cut and blunted at the PstI site. Plasmid pLM2064 was prepared from pLM1809 by exchanging the PstI/XbaI fragment at the 3′ terminus for the EcoRV/XbaI fragment from segment M.