Figure 6.

Synthesis of QA-induced products stops with removal of inducer, but progressive posttranslational modification of FRQ continues. (Upper) qa-2 mRNA arising from the normal sequence qa-2 promoter in the frq⁹qa-2pfrq strain is abundant in the presence of QA but rapidly disappears after removal of the inducer. The Northern blot was probed with the pqa-25′UTR riboprobe that recognizes only the qa-2 mRNA (see Materials and Methods). (Lower) Western blot analysis of corresponding frq⁹qa-2pfrq samples after removal of inducer shows FRQ to be abundant in the presence of QA and to drop slowly in concentration after the removal of inducer. Different exposures (2 min and 30 sec) of the Western blot allow the identification of the bands corresponding to the differentially modified FRQ products at different times. The position corresponding to the major (minimally modified) form of FRQ in the earliest samples is marked with an arrow. The absence of de novo synthesis accompanied by the progressive modification of FRQ is signaled by the gradual disappearance of predominant faster mobility (minimally modified) forms and the shift of FRQ to slower mobility forms.