Human satellite 3 (HS3) binding protein from the nuclear matrix: isolation and binding properties

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Satellite DNA (satDNA) constitutes a significant portion of residual DNA within nuclear matrix (NM) preparations.
• Nuclear matrix preparations are crucial for studying DNA organization and function within the nucleus.

Purpose of the Study:

• To identify and characterize proteins that specifically bind to human satellite 3 (HS3) DNA within the nuclear matrix.
• To determine the localization of HS3 DNA and its binding proteins within the nucleus.

Main Methods:

• Gel mobility shift assay (GMSA) to detect HS3 binding activity.
• Protein purification using DEAE-cellulose chromatography and preparative GMSA.
• DNase I footprinting and methylation interference assays to map binding sites.
• Antibody generation and immunofluorescence combined with fluorescent in situ hybridization (FISH) for localization studies.

Main Results:

• A specific HS3 binding activity was detected in nuclear matrix extracts.
• A 70 kDa protein (p70) was purified and identified as the primary HS3 binding protein.
• Binding sites were mapped to an AT-rich region within the HS3 fragment with a 10 bp periodicity.
• Immunofluorescence and FISH confirmed that p70 and HS3 DNA co-localize in heterochromatic regions surrounding nucleoli in interphase nuclei.

Conclusions:

• A specific 70 kDa protein (p70) binds to human satellite 3 (HS3) DNA within the nuclear matrix.
• This protein is localized to heterochromatic regions, suggesting a role in the structural organization of satellite DNA in the nucleus.