J Gen Virol
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J Gen Virol 5 (1969), 171-182; DOI 10.1099/0022-1317-5-2-171
© 1969 Society for General Microbiology
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Interconversion of rec+ and rec- Phenotype in {lambda} Lysogens of Escherichia coli

J. M. Erskine*

Medical Research Council Microbial Genetics Research Unit, Hammersmith Hospital, Ducane Road, London, W12

When a {lambda}-lysogenic recombination-deficient (rec-) mutant of Escherichia coli K12, AB 2463 ({lambda}), was superinfected with ultraviolet-irradiated {lambda} in the presence of 6-azauracil, there was found among surviving cells a doubly lysogenic form, AB 2463 ({lambda})(ind), with rec+ phenotype. The double lysogen obtained by superinfection of AB 2463 ({lambda}) with {lambda}cI 857 ind- displayed a rec- phenotype at 30° and rec+ characteristics at 40°. Superinfection of AB 2463 ({lambda}) with phage 434hy 2c+h, which lacks the c region of {lambda}, yielded rec- double lysogens. Since heat inactivation of the repressor in AB 2463 ({lambda}) ({lambda}cI 857 ind-) produced a rec+ form one of the prophages in AB 2463 ({lambda})(ind) may have been incompletely repressed, hence the expression of its recombination function. For its host-converting effect the superinfecting phage appeared to require the c region of its genome. The results of recombination analysis suggested that in AB 2463 ({lambda})(ind) the first prophage was integrated normally while the second prophage occupied a tandem position more distant than usual, and/or existed in a special relationship conferring on it immunity from or the capacity to overcome the repressor function of the cI product in respect of gene recombination function.

* Present address: New Zealand Dairy Research Institute, P.O. Box 1204, Palmerston North, New Zealand.

Received 5 June 1968; accepted 27 February 1969.




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Copyright © 1969 by the Society for General Microbiology.