Forms spikes that protrude from each vertex of the icosahedral capsid. Interacts with host receptor to provide virion initial attachment to target cell. Fiber proteins are shed during virus entry, when virus is still at the cell surface (By similarity). Homotrimer. Interacts (via N-terminal tail region) with pentons (By similarity). Anchored to the pentons, protrudes from the virion surface. Expressed in the late phase of the viral replicative cycle. The tail region anchors the fiber to penton base capsomers, whereas the shaft, built from several repeated motifs, allows the knob to protrude from the virion. All late proteins expressed from the major late promoter are produced by alternative splicing and alternative polyadenylation of the same gene giving rise to non-overlapping ORFs. A leader sequence is present in the N-terminus of all these mRNAs and is recognized by the viral shutoff protein to provide expression although conventional translation via ribosome scanning from the cap has been shut off in the host cell (By similarity). Belongs to the adenoviridae fiber family.