Molecular cloning and characterization of the complementary DNA and gene coding for the B-chain of subcomponent @entity6300 of the XXXX complement system.

@entity1 @entity1522 @entity2228 @entity6300 @entity535 @entity71016 @entity4022 @entity377
Plasmid clones containing cDNA coding for the B-chain of @entity1 Clq were isolated from a liver cDNA library. The longest cDNA insert isolated contained all the coding sequence for @entity535 residues B1 to B226 plus a 3' non-translated region of 264 nucleotides that extended into the poly(A) tail, thus accounting for 950 nucleotides of the mRNA. The B-chain mRNA was estimated by Northern-blot analysis to be 1.46 kb (kilobases) long, which indicated that approx. 500 bases were not accounted for in the cDNA clone. A cosmid clone containing the @entity71016 chain gene was isolated from a @entity1 genomic DNA library. The precise 5' limit of gene was not established, but from the data available it appears that the gene is approx. 2.6 kb long. The coding sequence for residues B1 to B226 in the gene is interrupted by one intron, of 1.1 kb, which is located within the codon coding for @entity2228 at position B36. This @entity2228 residue is located in the middle of the triple-helical regions found in @entity6300 at exactly the position where there is an unusual structural feature, i.e. a bend in each of the helical regions brought about by the interruption of the @entity4022 -Xaa-Yaa repeating triplet sequences in the A- and C-chains and the presence of an 'extra' triplet in the B-chain. @entity377 sequencing of the 5' end of the gene indicates the presence of a predominantly hydrophobic stretch of 29 @entity1522 , immediately before residue B1, which could serve as a signal peptide.
