Mapping and cloning of Eco RI-fragments of bacteriophage T5+ DNA

The Eco RI-fragments of bacteriophage T5 DNA were mapped using a technique which involves primarily length measurements of molecules observed in the electron microscope. Since Eco RI cleavage generates termini with 4-nucleotide long cohesive ends, fragments of complete and partial Eco RI digests were covalently circularized with DNA ligase at dilute DNA concentrations before measuring relative to internal length standards. This established the order of the internal Eco RI fragments. The two external Eco RI fragments, which had only one Eco RI terminus, were positioned relative to the internal fragments by identifying the location of some of the naturally-occurring nicks in partially denatured linear Eco RI fragments. An attempt was made to clone each of the internal Eco RI-fragments of T5 DNA via transformation into E. coli after ligation in vitro with the plasmid pMB 9. Only one fragment could be cloned and this fragment did not specify any new polypeptides in minicells of either the E. coli EK1 host, X1411, or the EK 2 host, X1776.