Figure 6.
Reduction of p50 binding correlates with premature translation. (A) A truncated EcoRI–DraI repressor RNA fragment shows a >10-fold decrease in p50 binding but Bruno binding is unaffected. A radioactive probe consisting of either the full-length repressor region (lanes 1–3) or a truncated form with 24 nucleotides deleted from the 5′ and 25 nucleotides from the 3′ (lanes 4–6) were incubated with oocyte extract in the presence of 100-fold molar excess of specific competitor (EcoRI–DraI fragment, lanes 2,5) or nonspecific competitor (polylinker of pSP72, lanes 3,6) and subsequently UV cross-linked. The same deletion mutation in the context of the first 380 nucleotides of the osk 3′ UTR had essentially the same effect on p50 and Bruno binding. The locations of the Bruno-binding consensus sequences with respect to the 5′ and 3′ truncations (light gray) are indicated below. (B) In vivo analysis of the effect of the 5′Δ24/3′Δ25 truncation of the proximal repressor element in an otherwise wild-type lacZ reporter gene (m1414lac5′Δ24/3′Δ25). The mutation does not affect RNA localization or levels of reporter transcripts (cf. with Fig. 2A, and see Fig. 7, lane 4,9); however, translation is detectable already from stage 6/7 onward.