The restriction mapping of c gene deletions in Streptomyces bacteriophage phi C31 and their use in cloning vector development.

In addition to 20 previously mapped restriction sites in the DNA of phi C31, we have determined eight sites for SphI, four for EcoRV, and two for SstII; there are none for BglII or SstI. Nine sites were in a 12-kb segment of DNA containing no previously mapped sites. Deletions causing clear-plaque morphology were located in this part of the DNA, in a 3-kb interval between an EcoRV and an SphI site at the centre of the DNA molecule. One of the deletions (delta C3) was obtained in a previously described phi C31c+::vph (viomycin phosphotransferase) derivative containing two PstI sites separated by 3.9-kb of inessential DNA. After in vitro PstI treatment, plaque-forming phages lacking the 3.9-kb fragment were obtained from the c+ phage but not from its delta C3 derivative. Thus a 36.2-kb genome, but not one of 34.4 kb, was able to give infectious virions. PstI-generated DNA fragments of up to 8 kb can be inserted in vitro into the delta C3 derivative with retention of the vph selective marker. With the insertion of a 6.03-kb PstI fragment of plasmid SCP2, the latter phage became a potential vector (with loss of vph) for BamHI-generated DNA fragments of up to 9 kb. In the course of this work, several ClaI sites in phi C31::pBR322 bifunctional replicons were shown to be lost when the DNA was propagated in a dam+ Escherichia coli strain. This will allow the use of such replicons for the cloning of ClaI-generated DNA fragments of up to 6.7 kb.