Yaba-like
disease virus (YLDV) is a yatapoxvirus, a group of slow-growing poxviruses from primates. Analysis of the growth cycle of YLDV in tissue culture showed that maximum virus titres were reached 3 days post-
infection and at this time only 3.3 % of infectious progeny was extracellular. The intracellular and extracellular virions have different buoyant densities and are separable on
CsCl density gradients. They are also distinguishable by electron microscopy with the extracellular virions having an additional
lipid envelope. In YLDV-infected cells, thick actin bundles with virions at their
tips were seen protruding from the cell surface, despite the fact that YLDV lacks a
protein comparable to Vaccinia virus A36R, which is required for VV-induced actin tail formation. In addition to these observations, the YLDV gene Y144R was characterized. This gene is predicted to encode a transmembrane
protein containing three short consensus repeat (SCR) motifs common to members of the
complement control
protein family. Antibody generated against recombinant Y144R recognized products of 36, 41 and 48-55 kDa in YLDV-infected cells and purified extracellular enveloped virus (EEV) but not intracellular mature virus (IMV). Y144R
protein is a
glycoprotein with type I membrane topology that is synthesized early and late during
infection. By immunoblot, indirect immunofluorescence and immuno-cryoelectron microscopy the Y144R
protein was detected on the intracellular enveloped virus (IEV), cell-associated enveloped virus (CEV) and EEV. This represents the first study of a YLDV IEV, CEV and EEV
protein at the molecular level.