The cDNA sequence of the β chain of lamprey Fibrinogen has been determined. To that end, an oligonucleotide probe was synthesized that corresponded to an amino acid sequence from the carboxy-terminal region of the lamprey fibrinogen β chain. The insert actually began with residue 3 of the fibrin β chain; it ran through to a terminator codon following the carboxy-terminal residue at position 443 and then continued for an additional 606 nucleotides of noncoding sequence to its 3' end. The inferred amino acid sequence was verified by comparison with assorted cyanogen bromide fragments isolated from the β-chain protein, including two carbohydrate-containing peptides that corresponded to segments containing the carbohydrate-attachment consensus sequence. Overall, the lamprey chain is 49% identical with the β chain from human fibrinogen. This is the same degree of resemblance as was found for the lamprey and human γ chains. Moreover, the principal regions of conservation are the same in both the β and γ chains. Differences and similarities in the physiological behavior of the two fibrinogens are assessed in terms of the observed amino acid replacements.
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