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About fifty suppressor sensitive (sus) mutants of phage ∅80 were isolated after hydroxylamine treatment, and these were classified into fourteen cistrons. In vitro and in vivo complementation experiments revealed that at least five cistrons were concerned with head formation and that at least six cistrons were concerned with tail formation in ∅80. Some presumed “early” mutants were also found. Defective lysogens were isolated from a ∅80-lysogenic nonpermissive strain using the colicin plate method (Gratia, 1966). In these strains deletions which affected the colicin B receptor gene extended for varying distances into prophage ∅80. Marker rescue experiments were carried out with these deletion lysogens by infecting various sus mutants, and the gene order in prophage ∅80 was determined. Clustering of all head genes and also of tail genes, as in phage λ, were demonstrated by the results of the prophage deletion mapping as well as the two-factor crosses performed among the sus mutants. Moreover, the gross gene arrangement of ∅80 was also similar to that of phage λ: namely, the cluster of head genes was found to be located at one end of the vegetative map of ∅80, being followed by that of tail genes, and presumed “early” genes are located at the other end of the map.

φ80 DNA prepared by a mild phenol extraction method had a buoyant density in a CsCl gradient of 1.710 g cm−3 and a thermal denaturation temperature of 90.5°. The buoyant density and thermal denaturation temperature of φ80pt1 DNA were identical to those of φ80 DNA. φ80 DNA had a guanine plus cytosine content of 53 mole per cent which was slightly higher than that of λ DNA or Escherichia coli DNA. The molecular weight of φ80 DNA estimated from the sedimentation rate was 29.3 × 106, and that of φ80pt1 DNA was 31.0 × 106. The significance of the observed difference in molecular weight between φ80 DNA and φ80pt1 is discussed.

Transducing variants of coliphage λ have been isolated from a donor strain in which the normal prophage-host relationship is altered by a deletion that extends from the galE gene of the host into the Q gene of the prophage. The 40 λ gal strains isolated fall into 8 classes. Two classes do not carry the deletion of the donor strain and must have arisen in the primary recipient. The most common class contains phage genes SR A-J and part of gene Q, and might arise by cutting at the att site. One class of λ gal contain all known λ genes except for a large section of gene Q. Lysogens of this class lyse late after induction, liberating a small amount of phage. A further mutation ( qin ) allows plaque formation by these Q-deletion phages, apparently by shortening the latent period. The qin mutation entails a physical loss of DNA, genetic loss of the gal genes and a loss of ability to complement genes S and R in trans .

The density of bacteriophage φ80 was measured by density gradient equilibrium centrifugation in CsCI solutions. This density was the same in phages derived from a lysogenic or a lytic growth cycle. The distribution of low-frequency transducing (LFT) particles of φ80 in a CsCl density gradient was shown to be much broader than that of plaque-forming particles. The transducing phages in the LFT lysates appear to transmit their characteristic densities, as well as definite try markers, to the φ80 dt particles in the high-frequency transducing lysates derived from them. The φ80 dt particles can be divided into two classes according to their requirement for helper phages in transduction. One class transduces more efficiently in the presence of active helper phage, while with the other class the active phage does not enhance or even reduces the transduction frequency. A new transducing phage type, which is not defective since it multiplies without help from the active phage, has been isolated. This phage, called φ80 pt (plaque-forming tryptophan), forms a small turbid plaque. A tryptophan auxotroph lysogenized by φ80 pt becomes try+, although it always segregates out some try− nonlysogenic cells. The buoyant density of φ80 pt in CsCI solution is greater than that of φ80, suggesting that a larger genetic fragment is carried in this phage.