TY - JOUR
T1 - The Arabidopsis Histone Chaperone FACT
T2 - Role of the HMG-Box Domain of SSRP1
AU - Pfab, Alexander
AU - Grønlund, Jesper T.
AU - Holzinger, Philipp
AU - Längst, Gernot
AU - Grasser, Klaus D.
PY - 2018/8/17
Y1 - 2018/8/17
N2 - Histone chaperones play critical roles in regulated structural transitions of chromatin in eukaryotic cells that involve nucleosome disassembly and reassembly. The histone chaperone FACT is a heterodimeric complex consisting in plants and metazoa of SSRP1/SPT16 and is involved in dynamic nucleosome reorganization during various DNA-dependent processes including transcription, replication and repair. The C-terminal HMG-box domain of the SSRP1 subunit mediates interactions with DNA and nucleosomes in vitro, but its relevance in vivo is unclear. Here, we demonstrate that Arabidopsis ssrp1–2 mutant plants express a C-terminally truncated SSRP1 protein. Although the structure of the truncated HMG-box domain is distinctly disturbed, it still exhibits residual DNA-binding activity, but has lost DNA-bending activity. Since ssrp1–2 plants are phenotypically affected but viable, the HMG-box domain may be functionally non-essential. To examine this possibility, SSRP1 ∆ HMG completely lacking the HMG-box domain was studied. SSRP1 ∆ HMG in vitro did not bind to DNA and its interactions with nucleosomes were severely reduced. Nevertheless, the protein showed a nuclear mobility and protein interactions similar to SSRP1. Interestingly, expression of SSRP1 ∆ HMG is almost as efficient as that of full-length SSRP1 in supporting normal growth and development of the otherwise non-viable Arabidopsis ssrp1–1 mutant. SSRP1 ∆ HMG is structurally similar to the fungal ortholog termed Pob3 that shares clear similarity with SSRP1, but it lacks the C-terminal HMG-box. Therefore, our findings indicate that the HMG-box domain conserved among SSRP1 proteins is not critical in Arabidopsis, and thus, the functionality of SSRP1/SPT16 in plants/metazoa and Pob3/Spt16 in fungi is perhaps more similar than anticipated.
AB - Histone chaperones play critical roles in regulated structural transitions of chromatin in eukaryotic cells that involve nucleosome disassembly and reassembly. The histone chaperone FACT is a heterodimeric complex consisting in plants and metazoa of SSRP1/SPT16 and is involved in dynamic nucleosome reorganization during various DNA-dependent processes including transcription, replication and repair. The C-terminal HMG-box domain of the SSRP1 subunit mediates interactions with DNA and nucleosomes in vitro, but its relevance in vivo is unclear. Here, we demonstrate that Arabidopsis ssrp1–2 mutant plants express a C-terminally truncated SSRP1 protein. Although the structure of the truncated HMG-box domain is distinctly disturbed, it still exhibits residual DNA-binding activity, but has lost DNA-bending activity. Since ssrp1–2 plants are phenotypically affected but viable, the HMG-box domain may be functionally non-essential. To examine this possibility, SSRP1 ∆ HMG completely lacking the HMG-box domain was studied. SSRP1 ∆ HMG in vitro did not bind to DNA and its interactions with nucleosomes were severely reduced. Nevertheless, the protein showed a nuclear mobility and protein interactions similar to SSRP1. Interestingly, expression of SSRP1 ∆ HMG is almost as efficient as that of full-length SSRP1 in supporting normal growth and development of the otherwise non-viable Arabidopsis ssrp1–1 mutant. SSRP1 ∆ HMG is structurally similar to the fungal ortholog termed Pob3 that shares clear similarity with SSRP1, but it lacks the C-terminal HMG-box. Therefore, our findings indicate that the HMG-box domain conserved among SSRP1 proteins is not critical in Arabidopsis, and thus, the functionality of SSRP1/SPT16 in plants/metazoa and Pob3/Spt16 in fungi is perhaps more similar than anticipated.
KW - chromatin
KW - DNA/nucleosome interaction
KW - histone
KW - HMG-box domain
KW - transcript elongation
UR - http://www.scopus.com/inward/record.url?scp=85049488802&partnerID=8YFLogxK
U2 - 10.1016/j.jmb.2018.06.046
DO - 10.1016/j.jmb.2018.06.046
M3 - Journal article
AN - SCOPUS:85049488802
SN - 0022-2836
VL - 430
SP - 2747
EP - 2759
JO - Journal of Molecular Biology
JF - Journal of Molecular Biology
IS - 17
ER -