Adeno-associated virus serotype 4 (AAV4) and AAV5 have different tropisms compared to AAV2 and to each other. We recently reported that ␣2-3 sialic acid is required for AAV5 binding and transduction. In this study, we characterized AAV4 binding and transduction and found it also binds sialic acid, but the specificity is significantly different from AAV5.

The adeno-associated viruses (AAVs) can package and deliver foreign DNA into cells for corrective gene delivery applications. The AAV serotypes have distinct cell binding, transduction, and antigenic characteristics that have been shown to be dictated by the capsid viral protein (VP) sequence. To understand the contribution of capsid structure to these properties, we have determined the crystal structure of AAV serotype 4 (AAV4), one of the most diverse serotypes with respect to capsid protein sequence and antigenic reactivity. Structural comparison of AAV4 to AAV2 shows conservation of the core ␤ strands (␤B to ␤I) and helical (␣A) secondary structure elements, which also exist in all other known parvovirus structures. However, surface loop variations (I to IX), some containing compensating structural insertions and deletions in adjacent regions, result in local topological differences on the capsid surface. These include AAV4 having a deeper twofold depression, wider and rounder protrusions surrounding the threefold axes, and a different topology at the top of the fivefold channel from that of AAV2. Also, the previously observed "valleys" between the threefold protrusions, containing AAV2's heparin binding residues, are narrower in AAV4. The observed differences in loop topologies at subunit interfaces are consistent with the inability of AAV2 and AAV4 VPs to combine for mosaic capsid formation in efforts to engineer novel tropisms. Significantly, all of the surface loop variations are associated with amino acids reported to affect receptor recognition, transduction, and anticapsid antibody reactivity for AAV2. This observation suggests that these capsid regions may also play similar roles in the other AAV serotypes.Adeno-associated viruses (AAVs), which are members of the Dependovirus genus of the Parvoviridae, are helper-dependent parvoviruses isolated from a number of different species, including humans (50). Despite a requirement for coinfection with a helper virus, such as adenovirus or herpesvirus, for productive replication, AAV capsids are similar to those of the autonomous parvoviruses, with Tϭ1 icosahedral symmetry and an overall diameter of ϳ260 Å that encapsulates a singlestranded-DNA (ssDNA) genome of ϳ5,000 bases (9,40,53,62,70). The capsid consists of three overlapping viral proteins (VPs), namely, VP1 (90 kDa), VP2 (72 kDa), and VP3 (60 kDa), at a ratio of 1:1:10, that are generated by alternative splicing and translational initiation during productive infection. VP3 constitutes 90% of the capsid, but all three proteins contain a common C-terminal domain of about 530 amino acids.Recombinant gene transfer vectors based on AAV serotype 2 (AAV2) have proven effective in animal models for the correction of genetic diseases of the eye, brain, muscle, liver, and lung (e.g., see references 18-20, 26, and 58), with human clinical trials now under way for the correction of several diseases. However, numerous studies, including those that use "pseudotyped" capsids, in which AAV vectors are generated usin...

We identify Xenopus NF-Y as a key regulator of acetylation responsiveness for the Xenopus hsp70 promoter within chromatin assembled in Xenopus oocyte nuclei. Y-box sequences are required for the assembly of DNase I-hypersensitive sites in the hsp70 promoter, and for transcriptional activation both by inhibitors of histone deacetylase and by the p300 acetyltransferase. The viral oncoprotein E1A interferes with both of these activation steps. We clone Xenopus NF-YA, NF-YB and NF-YC and establish that NF-Y is the predominant Y-box-binding protein in Xenopus oocyte nuclei. NF-Y interacts with p300 in vivo and is itself a target for acetylation by p300. Transcription from the hsp70 promoter in chromatin can be enhanced further by heat shock factor. We suggest two steps in chromatin modification at the Xenopus hsp70 promoter: first the binding of NF-Y to the Y-boxes to preset chromatin and second the recruitment of p300 to modulate transcriptional activity.