Adenovirus 3 fiber polypeptide gene: implications for the structure of the fiber protein

The nucleotide sequence of a 1,330-base-pair-long DNA segment located between map coordinates 88.5 and 92.3 in the adenovirus type 3 (Ad3) genome was determined. Transcripts from the r-strand of the region were mapped by S1 nuclease analysis and by in vitro translation of RNA, selected by filter hybridization. The results revealed that the sequenced region encodes the Ad3 fiber polypeptide with a molecular weight of 34,800. A comparison between the predicted amino acid sequences of the Ad3 and the Ad2 fiber polypeptides revealed that they have almost identical secondary structures, consisting of a tail, a shaft, and a knob. A striking difference between Ad2 and Ad3 fibers was that the shaft of the Ad3 fiber was significantly shorter, containing only 6 repeat units compared with 22 in the Ad2 fiber. The secondary structure suggests that the fiber is a dimeric structure, as proposed earlier (N.M. Green, N.G. Wrigley, W.C. Russell, S.R. Martin, and A.D. McLachlan, EMBO J. 2:1357-1365, 1983), with the size of the polypeptide determining the length of the fiber protein.