Bipartite mRNA for chicken alpha-fibrinogen potentially encodes an amino acid sequence homologous to beta- and gamma-fibrinogens.
Overlapping cDNAs derived from the chicken alpha-fibrinogen mRNA have been sequenced, beginning from within the coding region for the signal peptide of this subunit and terminating within the poly(A) extension. The predicted size of chicken alpha-fibrinogen is 54,187 daltons, which is the smallest of any alpha chain reported; the oligopeptide repeats that characterize the central regions of the other alpha subunits were conspicuously absent. A further unexpected finding was the presence on the mRNA of a separate, long open reading frame (752 nucleotides), beginning 312 nucleotides downstream from the alpha-fibrinogen coding sequence and containing intron-like features near its 5' end. The protein sequence predicted from this second open reading frame lacks an initiating methionine but is homologous to the C-terminal regions of all known beta- and gamma-fibrinogens as well as the C termini of two nonfibrinogen proteins: cytotactin (tenascin), an extracellular matrix protein, and pT49, a putative protein specific to cytotoxic T cells. The intron-like features of the second open reading frame immediately precede the region of common homology, and the beginnings of the corresponding homologous segments in the beta- and gamma-fibrinogen sequences are marked by aligned intron positions. Based on these findings, it is proposed that fibrinogen gene evolution included a fusion of two distinct ancestral genes.
Weissbach
L
L
Lindsley F. Kimball Research Institute, New York Blood Center, NY 10021.
Grieninger
G
G
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D002645:Chickens; D004247:DNA / Q000235:genetics; D015342:DNA Probes; D005340:Fibrinogen / Q000235:genetics*; D015723:Gene Library; D006801:Humans; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid
D015342:DNA Probes; D012333:RNA, Messenger; D005340:Fibrinogen; D004247:DNA