RS virus possesses two glycoproteins; a 84-88 kdal glycoprotein that lacks hemagglutinin and neuraminidase activities and is referred to as G. The other is a 68 kdal protein that is thought to be the fusion factor(FO); For is proteolytically cleaved into two subunits, F1 (48 kdal) and F2 (16 kdal). Since an amino acid sequence for these proteins is not available, we have attempted to deduce this sequence by a combination of recombinant DNA technology and DNA sequencing. A RS viral cDNA insert of 1755 bp hybridized to a vrial poly(A) RNA species 2000-2200 bases long. An RNA of this size was shown by Collins and Wertz to be translated in vitro to a 59 kdal protein, the putative unglycosylated translation progenitor of the 68 kdal viral fusion glucoprotein. The cDNA insert lacked a poly(A) tail. However, the messenger strand in the insert was established by primer extension of an asymmetrically 5' end labeled restriction fragment on mRNA from infected cells. Dideoxy-sequencing with this primer indicated that the recombinant lacked approximately 70 nucleotides corresponding to the 5' end of the mRNA. pRSA14 has single long open reading frame, starting at position 1 and ending at position 1671, that is capable of encoding a partial protein of 556 amino acids. Inspection of the amino acid sequence near the C-terminus revealed a 24 amino acid sequence extremely rich in hydrophobic residues followed by a 25 amino acid sequence rich in hydrophilic and polar residues extending all the way to the C-terminus of the protein.