Distinct Organization of DNA Complexes of Various HMGI/Y Family Proteins and Their Modulation upon Mitotic Phosphorylation

Abstract

High mobility group (HMG) proteins HMGI, HMGY, HMGI-C, and Chironomus HMGI are DNA-binding proteins thought to modulate the assembly and the function of transcriptional complexes. Each of these proteins contains three DNA-binding domains (DBD), properties of which appear to be regulated by phosphorylation. High levels of these proteins are characteristic for rapidly dividing cells in embryonic tissues and tumors. On the basis of their occurrence, specific functions for each of these proteins have been postulated. In this study we demonstrate differences in the nature of contacts of these proteins with promoter region of the interferon-␤ gene. We show that HMGI and HMGY interact with this DNA via three DBDs, whereas HMGI-C and Chironomus HMGI bind to this DNA using only two domains. Phos- Despite continuously increasing interest in the function(s) of this group of proteins, the nature of the interaction of these proteins with DNA is still not sufficiently understood. The proteins of the HMGI/Y family are 10 -11 kDa in size, are highly charged, are rich both in acidic and basic residues, are proline-rich, and contain only few residues with bulky hydrophobic side chains. This unusual amino acid composition inhibits folding of the polypeptide backbone of these proteins into any defined secondary structure. Common for HMGI/Y proteins is the presence of three putative DNA-binding domains (DBD), so called . NMR analysis of a complex of a peptide derived from HMGI(Y) bound to a short DNA fragment revealed that the centrally located RGR residues are essentially for binding and responsible for contacts of the protein with the bases and phosphate-sugar backbone (27). Alternative approaches, which used deletion and point-mutated proteins, revealed that two or three DBDs of the protein bind to DNA in a cooperative way (28 -30). Application of the protein-footprinting method for mapping of protein regions interacting with DNA (31) allowed more detailed characterization of the binding of HMGI(Y) proteins to DNA (32). A combination of this method

Cdk phosphorylation of the Ste11 transcription factor constrains differentiation-specific transcription to G1

“…Ste11 belongs to the family of HMGbox proteins, which are involved in many different differentiation processes (Soullier et al 1999). Interestingly, Cdk phosphorylation of HMGI/Y, belonging to the family of sequence-unspecific HMG-box proteins, was previously shown to prevent its binding to DNA (Reeves et al 1991;Piekielko et al 2001), although the biological significance of this remains to be demonstrated. It will be interesting to learn whether Cdk phosphorylation of transcription factors plays a general role in restricting differentiation-specific expression to G 1 .…”

A Mass Spectrometric Study on the in Vitro Methylation of HMGA1a and HMGA1b Proteins by PRMTs: Methylation Specificity, the Effect of Binding to AT-Rich Duplex DNA, and the Effect of C-Terminal Phosphorylation

“…Although all or only two (second and third AT-hooks) of the three AT-hooks are directly involved in DNA binding depending on the type of DNA substrates that have been examined, the second AT-hook plays a central role in the organization of the protein-DNA complexes (54)(55)(56)(57). Our results showed that, upon binding to AT-rich duplex DNA, the efficiencies of in vitro methylation of HMGA1 proteins by PRMT1, PRMT3, and PRMT6 were all markedly reduced ( Figure 3).…”

Identification and Characterization of a Tissue-Specific Coactivator, GT198, That Interacts with the DNA-Binding Domains of Nuclear Receptors

“…A recent report also indicates that the DBD of TR and retinoid X receptor (RXR) associates with PSF, a corepressor that recruits Sin3A to the receptor DBD (32). Another group of proteins that influence DNA binding of nuclear receptors is the high-mobility-group (HMG) proteins (7,8,38,43). In addition to facilitating the binding of nuclear receptors to DNA, HMG proteins have diverse regulatory functions in DNA binding and chromatin architecture (16).…”