Structural proteins of adenovirus-associated virus: subspecies and their relatedness

Capsids of adenovirus-associated virus (AAV) are known to contain three major structural proteins (A, B, and C). We have further resolved distinct subspecies of two of the major AAV proteins (two forms of protein A and four forms of protein C) which were found in both AAV1 and AAV2 serotypes. All subspecies were accurately synthesized in a cell-free translation system programmed with RNA isolated from infected cells. Analysis of virion proteins from the autonomous parvovirus H1 did not reveal a comparable array of subspecies of its major components. Staphylococcal V8 protease digestion of C proteins from AAV1 and AAV2 yielded very different electrophoretic patterns, indicating a considerable difference between the C proteins of these two serotypes, despite a high degree of genomic homology and an overall similarity in the number and relative proportions of analogous capsid proteins. On the other hand, staphylococcal V8 protease digestion of isolated proteins A, B, and C of AAV2 showed an extensive overlap among these proteins, possibly equivalent to all of protein C. In conjunction with other data, these findings suggest that proteins A, B, and C arise from different in-frame initiation sites contained in mRNA sequences that are transcribed from the right half of the AAV genome. The heterogeneity of subspecies may be explained by a partial read through of several tandem termination codons near the 3' end of AAV mRNA.