The effect of increasing doses of the 5′-UTR on
the activity of the I factor promoter. The vertical axis
indicates the CAT activity (pmol/min/mg of protein) in extracts of
ovaries from females obtained as indicated below. The horizontal axis
indicates the number of copies of the 5′-UTR per haploid genome.
Females of strains with 0, 2, 3, 5, or 10 copies of the 5′-UTR per
haploid genome were crossed with males carrying the 1–186:CAT reporter
gene. This gave progeny with 1, 3, 4, 6, or 11 copies of the 5′-UTR per
haploid genome. The black circles indicate the results of crosses using
females of strains C17H, P22H, and C17P22H whereas the white circles
indicate the results for strains C30H, P17H, and C30P17H. The final
point (11 copies) was obtained by using females of strain C17P22C30P17H
(Table 1).