Heterogeneous nuclear ribonucleoprotein D0B is a sequence-specific DNA-binding protein.

Area of Science:

• Molecular Biology
• Immunology
• Gene Regulation

Background:

• Complement receptor 2 (CR2) plays a critical role in regulating B lymphocyte responses.
• The precise regulation of CR2 gene expression is crucial for immune function.
• A 42 kDa heterogeneous nuclear ribonucleoprotein (hnRNP) was previously implicated in human CR2 gene transcriptional regulation.

Purpose of the Study:

• To identify and characterize the hnRNP involved in CR2 gene transcriptional regulation.
• To elucidate the DNA-binding properties and mechanism of action of this hnRNP.
• To determine the in vivo relevance of hnRNP D0B in CR2 gene transcription.

Main Methods:

• cDNA cloning of the involved hnRNP.
• Electrophoretic mobility-shift assays (EMSA) using mutated oligonucleotides.
• Determination of binding affinities (Kd) for double- and single-stranded DNA.
• In vivo co-precipitation assays with TATA-binding protein.

Main Results:

• The identified protein was hnRNP D0B, a sequence-specific RNA-binding protein.
• hnRNP D0B specifically binds to a double-stranded DNA motif within the CR2 promoter with an apparent Kd of 59 nM.
• hnRNP D0B exhibits significantly higher affinity for single-stranded DNA (28 nM sense, 18 nM anti-sense) compared to double-stranded DNA, suggesting DNA unwinding capability.
• hnRNP D0B interacts with the TATA-binding protein, a component of the basal transcription machinery.

Conclusions:

• hnRNP D0B functions as a sequence-specific DNA-binding protein that regulates CR2 gene transcription.
• The differential binding affinity for single- versus double-stranded DNA suggests a potential role in DNA melting during transcription initiation.
• hnRNP D0B interacts with basal transcription factors, indicating its role as a novel transcription factor in vivo.