A physical map of the permuted genome of bacteriophage T1.

A restriction map has been constructed for the DNA of coliphage T1 which locates the cleavage sites of the restriction endonucleases, BglI (6 cuts), BglII (16 cuts), EcoRI (2 cuts), HindIII (2 cuts) and PstI (2 cuts). Digestions with BglI and BglII reveal fragments which are present in sub-molar quantities. Two methods, one using the selective removal of molecular ends with exonuclease III and the other involving the comparison of digestion patterns of concatemeric and virion DNA, have shown that the submolar fragments are at or close to the ends of the molecules. Digestions with BglI show that one terminal fragment has a very precise molecular weight whereas all the others are of heterogenous molecular weight. These results are consistent with the model for DNA packaging in which maturation is initiated at a precise site on a concatemeric precursor and proceeds by the encapsidation of up to four successive 'headfuls' of 1.065 genome equivalents (MacHattie and Gill 1977).