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Isolation of cDNA clones specifying the fourth component of mouse complement and its isotype, sex-limited protein
Abstract:
cDNA clones specific for the fourth component of mouse complement (C4) and its hormonally regulated isotype, sex-linked protein (Slp), were isolated using as a probe a 20-mer synthetic oligonucleotide corresponding to a known sequence of human C4 cDNA. Two types of clones, one specific for C4 (pFC4/10, with a 3.7 kilobase insert) and one specific for Slp (pFSlp/1, with a 4.7 kilobase insert), were isolated from liver cDNA libraries constructed from the Slp-producing FM mouse strain. The cDNA inserts of these clones shared 70% of the restriction sites determined. Only one type of clone was isolated from the Slp-negative DBA/1 strain; this type showed restriction maps indistinguishable from that of pFC4/10. pFC4/10 and pFSlp/1 displayed extensive homology: 94% nucleotide homology and 89% derived amino acid homology in the C4a region and 92% nucleotide homology and 89% derived amino acid homology in the thiol-ester region. An Arg-Gln-Lys-Arg sequence in the beta-alpha junction and a Cys-Ala-Glu-Gln sequence in the thiol-ester site were identified for both proteins. A remarkable divergency between C4 and Slp sequences was recognized in the region immediately following the C4a sequence.
Insights
Researchers isolated cDNA clones for mouse complement component 4 (C4) and its sex-linked protein (Slp) isotype. High homology was found between C4 and Slp, with key sequence differences identified.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- The fourth component of complement (C4) is a crucial part of the immune system.
- Sex-linked protein (Slp) is a hormonally regulated isotype of C4.
- Understanding the genetic relationship between C4 and Slp is important for immunology.
Purpose of the Study:
- To isolate and characterize cDNA clones for mouse C4 and Slp.
- To investigate the sequence homology and divergence between C4 and Slp.
- To identify conserved and unique sequences within these related proteins.
Main Methods:
- Isolation of cDNA clones from mouse liver cDNA libraries using a human C4 cDNA probe.
- Restriction mapping of isolated cDNA inserts (pFC4/10 for C4, pFSlp/1 for Slp).
- Nucleotide and derived amino acid sequence analysis to determine homology.
Main Results:
- Two distinct cDNA clones, pFC4/10 (C4) and pFSlp/1 (Slp), were successfully isolated.
- High nucleotide (94% in C4a, 92% in thiol-ester region) and amino acid (89%) homology was observed between C4 and Slp.
- Conserved sequences (Arg-Gln-Lys-Arg, Cys-Ala-Glu-Gln) were identified in both proteins, alongside significant divergence in a specific region.
Conclusions:
- Mouse C4 and Slp are highly related gene products with significant sequence conservation.
- Specific sequence variations contribute to the distinct functional or regulatory properties of C4 and Slp.
- These findings provide insights into the evolution and functional diversification of complement components.