Similarity between the vaccinia virus 19K early protein and epidermal growth factor

An analysis of the 1,217-amino acid residue sequence of the precursor of mouse epidermal growth factor (mEGF) 1 revealed regions of considerable similarity with bovine factor X, a blood coagulation factor. Similarities of mEGF itself with factor X 2 , pancreatic secretory trypsin inhibitor 3 and, most strikingly, transforming growth factor I (TGF-I) 4,5 have been observed. On the basis of the comparisons described here, it seems that the presumptive 140-residue 19K early protein (relative molecular mass ( M r ) 19,000) of vaccinia virus 6 from residues 40–91 shows an overall identity of 36% (19/53 residues) with both mEGF and urogastrone (human epidermal growth factor, hEGF); a single deletion is assumed for vaccinia virus 19K protein which allows the six Cys residues (positions 45–80) to be aligned with those of mEGF or hEGF. This protein is encoded in the 10.3-kilobase (kb) inverted terminal repeat 6 . Because it is an early protein with an EGF-like central portion, the 19K vaccinia virus protein may have an autocrine function and may be required for DNA synthesis.