Behavior of prophage P1 in bacterial matings. I. Transfer of the defective prophage P1 dl

GENETIC INSTABILITY IN ESCHERICHIA COLI

Schwartz, Norman M. (Yale University, New Haven, Conn.). Genetic instability in Escherichia coli. J. Bacteriol. 89:712-717. 1965.-Results obtained from a transductional analysis demonstrated that an extremely unstable reversion of lac(-) is a suppressor mutation. This mutation suppresses 2 of 22 different lac(-) alleles tested. Five different Hfr strains transferred the suppressor soon after mating and at low frequency. Acridine orange enhanced the segregation of lac(-) clones from the unstable suppressed mutant. Stable suppressed lac(-) clones were produced by the unstable suppressed mutant. Two such stable suppressors were transferred at high frequency and mapped at different chromosomal sites on the basis of time of entry data. One of the stable suppressed lac(-) mutants reverted to the unstable suppressed lac(-) state. It is proposed that the suppressor is carried on an extrachromosomal element. The differences in stability observed may reflect differences in the state of the suppressor-bearing element.

Extrachromosomal inheritance in bacteria

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Intramolecular heterogeneity of the deoxyribonucleic acid of temperate bacteriophages

Spectral changes accompanying the thermal denaturation of phage deoxyribonucleic acid suggested that lambda is not unique in possessing large-scale intramolecular heterogeneity and nucleotide clustering; instead, lambda seems to share this property with other enteric phages.

Behavior of three colicine factors and an R (drug resistance) factor in Hfr crosses in Salmonella typhimurium

An LT2 Hfr strain,his metC gal, was crossed to a multiply marked LT2 F−line. Analysis of recombinant yields, segregation of unselected markers and interrupted matings indicated injection of the Hfr chromosome in the sequence

The introduction into the Hfr of the colicine factorscolI, colE1andcolE2and the R factorR2had little or no effect on its fertility. All four factors were transmitted at low frequency to the F−population, and to recombinants at higher frequencies (colI5–30%,colE130–80%,colE25–30%,R20–9%). Transfer ofcolE1occurred before 20 min., that ofcolE2andcolIlater than 100 min. Segregation data did not reveal close linkage of any factor to any chromosomal locus, but recombinants with a long stretch of donor chromosome were more likely than others to have acquiredcolE2andcolI. Nearly all recombinants andF−cells which acquiredcolIorcolE2acquired both, andcolE1also. Most cells which acquiredR2acquired one or more colicine factors. These plasmid associations can be formally represented by transfer of plasmids, independently of the chromosome, in the sequencecolE1—(colI, colE2)—R2. Phage P22 grown on the Hfr carrying the four plasmids transduced thetet-rtrait ofR2at very low frequency, and thesul-r str-rcharacters, together, at low frequency. Some of each sort of drug-resistance transductant, but no transductants in respect of chromosomal characters, acquiredcolEl or colE2by co-transduction.