A novel DNA-binding domain in theShrunken initiator-binding protein (IBP1)

Abstract

South-western screening of lambda gt11 expression library with a fragment of the Shrunken promoter containing the initiator element resulted in cloning of a novel maize gene. The encoded initiator-binding protein (IBP1) interacts at the transcription start site of the Shrunken promoter. Analysis of the 680 amino acid (aa) long polypeptide revealed a novel bipartite DNA-binding domain at the carboxyl terminus. In its amino-terminal part, it is weakly related to Myb R-repeats but the following basic region is also essential for DNA binding. A region of similarity to the conserved 2.1 and 2.2 motifs in bacterial sigma-factors is located close to the IBP1 amino terminus. Two putative nuclear localization signals are compatible with the presence of antigenically related polypeptides in nuclear protein extracts. The IBP1 gene was mapped to the long arm of chromosome 9 (9L095); a second highly related gene IBP2 is located on the short arm of chromosome 1 (1S014). Both genes encode proteins sharing 93% similarity and are transcribed with similar activity in different plant organs. A small 82 nucleotide intron in the IBP2 transcript is found unspliced to a variable degree in different tissues. Translation of this incompletely processed transcript would result in a truncated amino-terminal polypeptide lacking the DNA-binding domain.

A C-terminal Myb Extension Domain Defines a Novel Family of Double-strand Telomeric DNA-binding Proteins in Arabidopsis

“…Interestingly, maize IBP1 (initiator-binding protein 1 and the parsley BPF1 (BoxP-binding factor 1 (BPF1) also harbor a Myb domain (52,53) with an adjacent region having striking similarity to Mybext. 4 IBP1 is known to interact at the transcription start site of the Shrunken promoter containing a perfect telomeric repeat, AGGGTTT, whereas BPF1 binds a series of GT-rich motifs.…”

PcMYB1, a novel plant protein containing a DNA‐binding domain with one MYB repeat, interacts in vivo with a light‐regulatory promoter unit

“…The N-terminal region of PcMYB1 exhibits a striking sequence similarity to the R1, R2 and R3 repeats of the animal MYB proteins as well as the R2 and R3 repeats et al, 1993), IBP1 (Lugert and Werr, 1994), TRF (Chong et al, 1995), TBF1 (Brigati et al, 1993), RAP1 (KOnig et al, 1996), XMYB1 (Bouwmeester et al, 1992), cMYB (Gonda eta/., 1985), C1 (Paz-Ares et al, 1987), GL-1 (Oppenheimer et al, 1991), MYB305 (Jackson eta/., 1991), and MYBST1 (Baranowskij et al, 1994). On the right, the percentage of sequence identity in the compared areas is given.…”

“…Two ORFs given in the dbEST database (designated AtMYB1-2 and OsMYB1; Figure 3) and four MYB-like DNAbinding proteins share this DNA-binding domain with PcMYBI: BPF1 from P. crispum binds MREPAL-p of the PcPAL 1 promoter (da Costa e Silva et al, 1993); IBP1 from Z. mays binds the initiator sequence of the Shrunken promoter and is thought to play a role in basal expression (Lugert and Werr, 1994); TRF recognizes the (TTAGGG) n sequence from Homo sapiens telomers and has been shown by elegant studies to be a component of human telomers (Chong et al, 1995); and TBF1 from Saccharomyces cerevisiae, which is essential for growth, binds in vitrotelomeric sequences of mammals and slime moulds (Bilaud et aL, 1996;Brigati et aL, 1993).…”

Molecular Evolution of the Myb Family of Transcription Factors: Evidence for Polyphyletic Origin

“…The Myb domain occurs as consecutive tandem repeats of about 50 amino acids located near the protein's amino terminus (Howe et al 1990;Sakura et al 1989). There are generally three repeats in animals and two in plants, although proteins have been identified that contain only a single repeat unit (Baranowskij et al 1994;da Costa et al 1993;Lugert and Werr 1994). Critical in the formation of the tertiary structure of the conserved Myb motif is a series of constantly spaced tryptophan residues (Anton and Frampton 1988;Kanei-Ishii et al 1990).…”