AHM1, a Novel Type of Nuclear Matrix-Localized, MAR Binding Protein with a Single AT Hook and a J Domain-Homologous Region

Abstract

Interactions between the nuclear matrix and special regions of chromosomal DNA called matrix attachment regions (MARs) have been implicated in various nuclear functions. We have identified a novel protein from wheat, AT hookcontaining MAR binding protein1 (AHM1), that binds preferentially to MARs. A multidomain protein, AHM1 has the special combination of a J domain-homologous region and a Zn finger-like motif (a J-Z array) and an AT hook. For MAR binding, the AT hook at the C terminus was essential, and an internal portion containing the Zn finger-like motif was additionally required in vivo. AHM1 was found in the nuclear matrix fraction and was localized in the nucleoplasm. AHM1 fused to green fluorescent protein had a speckled distribution pattern inside the nucleus. AHM1 is most likely a nuclear matrix component that functions between intranuclear framework and MARs. J-Z arrays can be found in a group of (hypothetical) proteins in plants, which may share some functions, presumably to recruit specific Hsp70 partners as co-chaperones. INTRODUCTIONThe nuclear matrix, operationally defined, is the dynamic fibrogranular structure forming the skeletal framework that surrounds and penetrates the interphase nucleus; it has been implicated in most nuclear functions, including replication, repair, transcription, RNA processing, and RNA transport (Berezney and Jeon, 1995). The chromosomal DNAs are known to be associated with the nuclear matrix at specific regions called matrix attachment regions (MARs) and are thereby thought to be organized into topologically constrained loops, each of which represents a sort of functional or structural domain (or both) (Laemmli et al., 1992;Bode et al., 1996). In animals, interactions between the nuclear matrix and MARs have also been shown to be involved in DNA replication and repair and in various aspects of gene regulation, thus playing a key role in the essential functions of the nucleus (Boulikas, 1995;Bode et al., 1996).MARs consist of AT-rich sequences extending over at least a few hundred base pairs and containing various ATrich motifs as well as structural motifs such as base-unpairing regions and intrinsically curved portions (Boulikas, 1995). In animals, MAR binding activity has been found in a wide range of structurally and functionally diverse proteins (listed in Boulikas, 1995). These include topoisomerase II (Adachi et al., 1989); filament proteins such as lamins and NuMA (Ludérus et al., 1992(Ludérus et al., , 1994; ARBP, identical to a methylated CpG binding protein (von Kries et al., 1991;Weitzel et al., 1997); hnRNP-U/SAF1, an RNA binding protein involved in RNA processing (Fackelmayer et al., 1994;von Kries et al., 1994); SATB1, a tissue-specific transcription factor with high affinity for base-unpairing regions (Dickinson et al., 1992; de Belle et al., 1998); and architectural chromatin proteins such as histone H1 and HMG-I/Y (Zhao et al., 1993).In plants, MARs have been found in intergenic regions, often in or close to the regulatory regions of genes, and clo...

Functional Isolation of Novel Nuclear Proteins Showing a Variety of Subnuclear Localizations

“…The OsAHP1, a probable HMG I/Y-related chromatin protein containing an AT-Hook motif, is localized in a chromatin region similar to the wheat (Triticum aestivum) MAR binding protein AHM1 (Morisawa et al, 2000). Detailed analysis of the subnuclear localization of the fusion protein showed uneven distribution overlapping the DAPI stain ( Figures 5E to 5H), suggesting an association of OsAHP1 with some specific regions of the chromatin structure.…”

Cell-to-Cell Movement of Two Interacting AT-Hook Factors inArabidopsisRoot Vascular Tissue Patterning

“…One of them was shown to have specific binding activity to DNA elements, which is required for the expression of a direct target gene (Matsushita et al, 2007). AThook members were also shown to bind the matrix attachment regions in the nuclei (Morisawa et al, 2000;Fujimoto et al, 2004;Lim et al, 2007;Ng and Ito, 2010).…”

BARREN STALK FASTIGIATE1 Is an AT-Hook Protein Required for the Formation of Maize Ears

“…AT-hook transcriptional regulators are generally considered architectural transcriptional regulators, making chromatin more accessible for DNA binding, possibly through structural changes. They are predicted to bind AT-rich DNA regions, such as the matrix attachment regions, putative structural components of nuclei (Morisawa et al, 2000;Fujimoto et al, 2004). Several AT-hook DNA binding proteins with a similar domain organization to BAF1 have been described in plants.…”