Arabidopsis chromatin-associated HMGA and HMGB use different nuclear targeting signals and display highly dynamic localization within the nucleus.
In plants, the chromatin-associated high mobility group (HMG) proteins occur in two subfamilies termed HMGA and HMGB. The HMGA proteins are characterized by the presence of four AT-hook DNA binding motifs, and the HMGB proteins contain an HMG box DNA binding domain. As architectural factors, the HMG proteins appear to be involved in the regulation of transcription and other DNA-dependent processes. We have examined the subcellular localization of Arabidopsis thaliana HMGA, HMGB1, and HMGB5, revealing that they localize to the cell nucleus. They display a speckled distribution pattern throughout the chromatin of interphase nuclei, whereas none of the proteins associate with condensed mitotic chromosomes. HMGA is targeted to the nucleus by a monopartite nuclear localization signal, while efficient nuclear accumulation of HMGB1/5 requires large portions of the basic N-terminal part of the proteins. The acidic C-terminal domain interferes with nucleolar targeting of HMGB1. Fluorescence recovery after photobleaching experiments revealed that HMGA and HMGB proteins are extremely dynamic in the nucleus, indicating that they bind chromatin only transiently before moving on to the next site, thereby continuously scanning the genome for targets. By contrast, the majority of histone H2B is basically immobile within the nucleus, while linker histone H1.2 is relatively mobile.
Launholt
Dorte
D
Department of Life Sciences, Aalborg University, DK-9000 Aalborg, Denmark.
Merkle
Thomas
T
Houben
Andreas
A
Schulz
Alexander
A
Grasser
Klaus D
KD
D024761:AT-Hook Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D024361:Amino Acids, Basic / Q000378:metabolism; D017360:Arabidopsis / Q000166:cytology / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D002843:Chromatin / Q000378:metabolism*; D032461:Chromosomes, Plant / Q000378:metabolism; D018744:DNA, Plant / Q000378:metabolism; D036681:Fluorescence Recovery After Photobleaching; D049452:Green Fluorescent Proteins / Q000378:metabolism; D024003:HMGA Proteins / Q000737:chemistry / Q000378:metabolism*; D024002:HMGB Proteins / Q000737:chemistry / Q000378:metabolism*; D024243:HMGB1 Protein / Q000737:chemistry / Q000378:metabolism*; D006657:Histones / Q000378:metabolism; D007399:Interphase; D008938:Mitosis; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals / Q000378:metabolism; D021381:Protein Transport; D011523:Protoplasts / Q000166:cytology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D036226:Seedlings / Q000166:cytology; D015398:Signal Transduction; D014026:Nicotiana / Q000166:cytology
D024361:Amino Acids, Basic; D029681:Arabidopsis Proteins; D002843:Chromatin; D018744:DNA, Plant; D024003:HMGA Proteins; D024002:HMGB Proteins; D024243:HMGB1 Protein; C517312:HMGB1 protein, Arabidopsis; C517313:HMGB5 protein, Arabidopsis; D006657:Histones; D019913:Nuclear Localization Signals; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins