Genetic recombination in DNA-induced transformation of Pneumococcus. IV. The pattern of transmission and phenotypic expression of high and low-efficiency donor sites in the amiA locus.

HE mode of onset of transmission of a gene acquired through DNA-induced transformation will necessarily reflect some features of the process of genetic recombination in bacterial transformation systems. In an earlier publication, a method was briefly described 'which permitted the determination of when, on the average, a newly acquired gene begins to be transmitted at cell division, in Diplococcus pmumoniae ( EPHRUSSI-TAYLOR 1958) . This procedure consists in splitting apart sister cocci formed at successive divisions of synchronously dividing transforming cultures, and scoring the numbers of cocci bearing the acquired gene. A coccus is considered to bear the newly acquired gene if it has the potential to give rise to a phenotypically transformed clone, irrespective of whether the phenotype is expressed at the time of splitting. The present paper describes the method in greater detail than has hitherto been done, and presents a detailed quantitative study of two different genes, the one (str-r41) showing a high efficiency as a transforming factor, and the other (opt-r2) showing a low efficiency (HE and LE genes, respectively). These two genes, introduced into a single population of recipient cells, show different modes of transmission: the opt-r gene is, apparently, always transmitted to both progeny at the second division following DNA uptake, while the str-r41 gene is usually transmitted to both progeny only at the third division. Using these two genes for reference, the transmission pattern of other genes acquired through transformation can be established by determining the ratios of transformants bearing these genes to those bearing the reference genes, in sonically treated cell suspensions made after one, two, or more divisions. It has been established ih this way that five mutant sites of the amiA locus, all showing low efficiency as transforming factors, are transmitted in the manner of the opt-r2 gene, whereas four mutant sites of the same locus, all showing high efficiency, are transmitted in the manner of the str-r41 gene. The transmission pattern of the opt-r2 marker gene