Isolation and characterization of an Escherichia coli strain harboring three sex factors.

I N 1963, CLARK reported the isolation of a double male strain of Escherichia coli K12. This strain is singular in that it transfers its genetic material to recipients during conjugation in an oriented manner in the form of two nonhomologous linkage groups. In explaining the behavior of the double male, CLARK (1963) favored the model of a haploid homokaryon with two sex factors integrated along the same chromosome with alternative leading origins in conjugation. One sex factor (denoted Fa in this paper) promotes transfer with the sequence O-strmal-xyl . . . met-Fb and the other sex factor (denoted Fb) promotes transfer with the sequence 0-thr-leu-pro-lac . . . serA-Fa. The present paper reports experiments in which an F-merogenote (F30) has been successfully implanted in the double male. The characteristics of this strain and the F30 element it carries will be described and interpreted. A preliminary account of this work has been reported previously (BASTARRACHEA 1967).