The Hedgehog signaling pathway is involved in both development and cancer induction in a wide range of organisms. The end point of the Hedgehog signal-transduction cascade is the Gli/Ci, zinc-finger transcription factors. Proteins such as Fused, Suppressor of fused (SUFU), Costal-2, and protein kinase A are essential for regulation of Gli/Ci processing, activity, and localization. Coimmunoprecipitation and Far Western assays, coupled with truncation analysis and mutagenesis have been used to define the region of interaction between Gli proteins and SUFU. We identify a novel motif SYGH in Gli/Ci family proteins, which is required for the interaction with SUFU. Mutational studies revealed that Gly 122 and His 123 are crucial for binding to SUFU, suggesting the importance of hydrophobicity for the correct binding conformation. Functional analysis revealed that the activity of GLI transcription factors with mutations in this motif is no longer suppressed by coexpression of SUFU. Moreover, we have found that a C-terminal 19-amino acid deletion in SUFU (⌬465) is sufficient to abrogate interaction with GLI1. Interestingly, this SUFU mutant localizes in the nucleus, most probably because it is not efficiently sequestered in the cytoplasm. Taken together, we identified a novel motif in the Gli/Ci family of proteins that is essential both for protein-protein interaction with SUFU and for functional repression of GLI1 by SUFU.

The early light-induced proteins (Elips) in higher plants are nuclear-encoded, light stress-induced proteins located in thylakoid membranes and related to light-harvesting chlorophyll (LHC) a/b-binding proteins. A photoprotective function was proposed for Elips. Here we showed that after 2 h exposure of Arabidopsis (Arabidopsis thaliana) leaves to light stress Elip1 and Elip2 coisolate equally with monomeric (mLhcb) and trimeric (tLhcb) populations of the major LHC from photosystem II (PSII) as based on the Elip:Lhcb protein ratio. A longer exposure to light stress resulted in increased amounts of Elips in tLhcb as compared to mLhcb, due to a reduction of tLhcb amounts. We demonstrated further that the expression of Elip1 and Elip2 transcripts was differentially regulated in green leaves exposed to light stress. The accumulation of Elip1 transcripts and proteins increased almost linearly with increasing light intensities and correlated with the degree of photoinactivation and photodamage of PSII reaction centers. A stepwise accumulation of Elip2 was induced when 40% of PSII reaction centers became photodamaged. The differential expression of Elip1 and Elip2 occurred also in light stress-preadapted or senescent leaves exposed to light stress but there was a lack of correlation between transcript and protein accumulation. Also in this system the accumulation of Elip1 but not Elip2 correlated with the degree of PSII photodamage. Based on pigment analysis, measurements of PSII activity, and assays of the oxidation status of proteins we propose that the discrepancy between amounts of Elip transcripts and proteins in light stress-preadapted or senescent leaves is related to a presence of photoprotective anthocyanins or to lower chlorophyll availability, respectively.