Identification of a partial cDNA clone for the human receptor for complement fragments C3b/C4b

Area of Science:

• Molecular Biology
• Immunology
• Genetics

Background:

• The human complement receptor type 1 (CR1) plays a crucial role in immune regulation by binding complement fragments C3b/C4b.
• Understanding the genetic basis of CR1 polymorphism is essential for comprehending its functional variations and associated diseases.

Purpose of the Study:

• To isolate and characterize the cDNA encoding human CR1.
• To investigate the molecular basis of CR1 protein polymorphism.
• To elucidate the gene structure and identify potential CR1 gene family members.

Main Methods:

• Synthesis of redundant oligonucleotide probes based on CR1 tryptic peptide sequences.
• Screening of a human tonsilar cDNA library using these probes.
• Nucleotide sequencing of positive cDNA clones.
• Northern and Southern blot analyses to study CR1 gene expression and structure.

Main Results:

• Identification of a 1.5 kb CR1 cDNA clone containing homologous sequences to CR1 peptides.
• Detection of two CR1 mRNA species (9 and 11 kb) in human tonsil mRNA.
• Southern blot analysis revealed complex restriction patterns suggesting homologous domains or multiple CR1 genes.
• Association of a specific BamHI fragment with the CR1 S allotype, indicating nucleotide sequence differences underlie protein polymorphism.

Conclusions:

• The study successfully isolated a CR1 cDNA, providing insights into its molecular structure.
• CR1 gene exhibits significant structural complexity, potentially involving multiple genes or homologous domains.
• Polymorphism in CR1 protein variants is directly attributable to variations in nucleotide sequences within the CR1 gene(s).