STF1 is a novel TGACG‐binding factor with a zinc‐finger motif and a bZIP domain which heterodimerizes with GBF proteins

Abstract

SummaryTwo separate nuclear binding activities (B1 and B2) in the soybean apical hypocotyl have been identified that interact with a palindromic C-box sequence (TGACGTCA) and which are developmentally regulated in an inverse manner. The bZIP factors responsible for these two binding activities, B1 and B2, were isolated from a cDNA library and designated STGA1 and STFs (STF1 and STF2), respectively. Sequence analysis shows that the STFs contain both a zinc-finger domain and a bZIP domain. The two zinc finger sequences of Cys 4 -Cys 4 are most related to the RING zincfinger motif carrying a Cys 3 -His-Cys 4 . In addition the bZIP domain of STFs is highly homologous to the HY5 protein of Arabidopsis. DNA binding studies revealed that STF1 binding to the TGACGT sequence requires distinct flanking sequences. Furthermore, STF1 binds to the Hex sequence as a heterodimer with G-box binding factors (GBFs), a feature not observed with STGA1. Since STF1 expression is most prevalent in apical and elongating hypocotyls, it is proposed that STF1 may be a transcription factor involved in the process of hypocotyl elongation.

DNA-Binding Study Identifies C-Box and Hybrid C/G-Box or C/A-Box Motifs as High-Affinity Binding Sites for STF1 and LONG HYPOCOTYL5 Proteins

“…STF1 has the unusual feature of having two unrelated structural domains with high-sequence homology to the N-terminal RING-finger domain found in RADIALLY SWOLLEN1 (RSW1): the cellulose synthase catalytic subunit and the C-terminal HY5-like bZIP domain. The bZIP proteins show a similar structural feature found in other legume bZIP proteins, including broad bean (Vicia faba) VFBZIPZF and Lotus japonicus LjBZF (Cheong et al, 1998;Nishimura et al, 2002). The role of LjBZF, a gene product of ASTRAY, was predicted in astray (Ljsym77), a root mutant that develops an increased number of nodules compared with the wild type.…”

“…Error bars represent the SD. [See online article for color version of this figure.] Cheong et al, 1998). When STF1 and HY5 are compared, the full-length STF1 possesses weaker binding activity than HY5 to both the PA G-and the CHS-U1 G-boxes (Fig.…”

“…Altogether, the transgenic plant analysis provides further support that STF1 and HY5 have the same role in photomorphogenesis and hormone signaling. binding site (Cheong et al, 1998). The HY5 protein interacts with both the G-(CACGTG) and Z-(ATACGTGT) boxes of the light-regulated promoter of RbcS1A (ribulose bisphosphate carboxylase small subunit) and the CHS (chalcone synthase) genes Chattopadhyay et al, 1998;Yadav et al, 2002).…”

“…3A). C-box sequences carrying the mammalian cAMP responsive element (CRE; TGACGTCA) motif and the Hex sequence (TGACGTGGC), a hybrid C/G-box (Cheong et al, 1998), were high-affinity binding sites for both proteins (Fig. 3B).…”

“…Previously, STF1, a homologous bZIP protein that acts as a potential regulatory factor for hypocotyl elongation, was reported for soybean (Glycine max; Cheong et al, 1998). STF1 has the unusual feature of having two unrelated structural domains with high-sequence homology to the N-terminal RING-finger domain found in RADIALLY SWOLLEN1 (RSW1): the cellulose synthase catalytic subunit and the C-terminal HY5-like bZIP domain.…”