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Messenger RNA coding for the deleted heavy chain of mouse myeloma MOPC 47A immunoglobulin
Abstract:
Mouse IgA 47A is an immunoglobulin variant whose heavy (alpha) chain has a molecular weight of 40,000 and lacks the entire CH3 domain. In order to understand better the mechanism by which the CH3 domain is lost, the 47A heavy chain mRNA has been partially purified. The mRNA migrated as a 17 S species on sucrose gradients and coded for the cell-free synthesis of only one serologically reactive protein with an apparent molecular weight of 42,000. Competitive inhibition of immunoprecipitation and tryptic peptide analysis of a cyanogen bromide fragment of the in vitro product revealed significant homology between the authentically secreted heavy chain and the respective cell-free synthesized, immunoprecipitated product. The heavy chain mRNA of 47A possessed a chain length of about 2200 nucleotides which is the same size as a normal alpha heavy chain mRNA, thus demonstrating that the protein deletion is not due to a large deletion at the mRNA level. The deletion in the 47A heavy chain may be due to a frameshift of a single nucleotide followed by premature chain termination.
Insights
Researchers investigated a mouse immunoglobulin A (IgA) variant lacking the CH3 domain. The study suggests a single nucleotide frameshift in the heavy chain mRNA may cause this deletion, not a large mRNA alteration.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- Immunoglobulin A (IgA) is a crucial antibody isotype.
- The 47A variant of mouse IgA features a heavy (alpha) chain lacking the CH3 domain.
- Understanding the molecular basis of IgA structural variations is important for immunology.
Purpose of the Study:
- To investigate the molecular mechanism behind the loss of the CH3 domain in the 47A mouse IgA heavy chain.
- To determine if the protein deletion results from alterations at the mRNA level.
Main Methods:
- Partial purification of 47A heavy chain messenger RNA (mRNA).
- Sucrose gradient sedimentation to analyze mRNA size.
- Cell-free protein synthesis to translate the mRNA.
- Competitive inhibition of immunoprecipitation and tryptic peptide analysis to compare synthesized and native proteins.
Main Results:
- The 47A heavy chain mRNA is a 17S species, coding for a 42,000 Da protein.
- Analysis confirmed homology between the cell-free synthesized product and the authentic IgA heavy chain.
- The mRNA size (approx. 2200 nucleotides) is comparable to normal alpha heavy chain mRNA.
Conclusions:
- The deletion of the CH3 domain in 47A mouse IgA heavy chain is not due to a large deletion in the mRNA.
- A potential mechanism involves a single nucleotide frameshift in the heavy chain mRNA, leading to premature chain termination.