The above hand-written note by Esther M. Zimmer Lederberg
can be found in her copy of "The Eighth Day of Creation:
The Makers of the Revolution in Biology", by Judson, H. F.,
Simon and Schuster, New York, 1979, p. 386.
"F, fertility factor" is also used by M. L. Morse, for example,
in his Feb. 1962 paper, "Spontaneous Production of Lambda Particles
with Transducing Activity", Genetics, 47, #2, 255-258;
p. 255 (citing Esther Lederberg, only, p. 258)
"Another infectious particle that has jumped out of our Pandora's
box determines the very capacity of E. coli to function as
a male partner in fertilization (51). For lack of a better inspiration,
we call this particle "F". Two kinds of male strains are now recognized
according to whether the F particle has a chromosomal or a cytoplasmic
location. F+ strains, like the original K-12, are highly contageous for
F and will rapidly convert populations of female, F– strains in
which they are introduced. Hfr males, on the other hand, have a
chromosomal localization of the F factor resulting from occasional
transpositions in F+ strains.", "Les Prix Nobel en 1958", Stockholm,
Imprimerie Royal P. A. Norstedt & Söner, 1959, p. 183. Nobel Prize
award speech by Dr. J. Lederberg.
Note the "vague" lack of knowledge of what gave rise to the nomenclature.