Identification and characterization of PF4varl, a human gene variant of platelet factor 4.
A synthetic DNA probe designed to detect coding sequences for platelet factor 4 and connective tissue-activating peptide III (two human platelet alpha-granule proteins) was used to identify several similar sequences in total human DNA. Sequence analysis of a corresponding 3,201-base-pair EcoRI fragment isolated from a human genomic library demonstrated the existence of a variant of platelet factor 4, designated PF4var1. The gene for PF4var1 consisted of three exons and two introns. Exon 1 coded for a 34-amino-acid hydrophobic leader sequence that had 70% sequence homology with the leader sequence for PF4 but, in contrast, contained a hydrophilic amino-terminal region with four arginine residues. Exon 2 coded for a 42-amino-acid segment that was 100% identical with the corresponding segment of the mature PF4 sequence containing the amino-terminal and disulfide-bonded core regions. Exon 3 coded for the 28-residue carboxy-terminal region corresponding to a domain specifying heparin-binding and cellular chemotaxis. However, PF4var1 had amino acid differences at three positions in the lysine-rich carboxy-terminal end that were all conserved among human, bovine, and rat PF4s. These differences should significantly affect the secondary structure and heparin-binding properties of the protein based on considerations of the bovine PF4 crystal structure. By comparing the PF4var1 genomic sequence with the known human cDNA and the rat genomic PF4-coding sequences, we identified potential genetic regulatory regions for PF4var1. Rat PF4 and human PF4var1 genes had identical 18-base sequences 5' to the promoter region. The intron positions appeared to correspond approximately to the boundaries of the protein functional domains.
Green
C J
CJ
Molecular Biology Department, SRI International, Menlo Park, California 94025.
Charles
R S
RS
Edwards
B F
BF
Johnson
P H
PH
D000595:Amino Acid Sequence; D001483:Base Sequence; D004247:DNA / Q000235:genetics; D015342:DNA Probes; D014644:Genetic Variation; D006801:Humans; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics; D010978:Platelet Factor 4 / Q000235:genetics*; D021382:Protein Sorting Signals / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid; D012689:Sequence Homology, Nucleic Acid
D015342:DNA Probes; D010455:Peptides; D021382:Protein Sorting Signals; D010978:Platelet Factor 4; C009862:connective tissue-activating peptide; D004247:DNA