Mechanisms Mediating Nuclear Trafficking Involved in Viral Propagation by DNA Viruses

Figure 1. Schematic representation of the nucleocytoplasmic shuttling of viral proteins and particles.

Figure 2. Distribution of green fluorescence signal in BmN cells transfected with a transient expression vector. (A) Effect of mutations in the motifs of 33RRIK and 76KRKCSK of Bm65 on the subcellular localization of the Bm65–EGFP fusion protein. Compared with the wild type (WT) and the mutation in 33RRIK of Bm65, the mutations in the motif of 76KRKCSK block the nuclear import of Bm65. (B) Effect of N-deletion of BmBDV NS1 on subcellular localization of the NS1–EGFP fusion protein. Compared with NS1–EGFP, deletions of the N-terminal of BmBDV NS1 impaired the nuclear import of NS1. The WT indicates the amino acid sequence of Bm65 WT. EGFP indicates enhanced green fluorescence protein. The amino acids of RRIK were mutated into 33AAAA, and 76KRKCSK into 76AAACSA in the mutant type (MT) of Bm65. WT BmBDV NS1 consists of 316 amino acids (aa), with 291 aa and 216 aa indicating the deletion of 25 and 100 amino acids from the N-terminal of BmBDV NS1, respectively.

Figure 3. Multiple sequence alignment showed that basic amino acid clusters, corresponding to potential NLSs, are found in viral capsid sequences. Some single amino acids (lysine (R) and arginine (K)) are highly conversed in these sequences, which are potentially involved in nuclear import. These sequences are from GenBank, and their accession numbers are as follows: cutavirus (AMS35095.1), Wuharv parvovirus (AFV48070.1), primate protoparvovirus (YP_009507380.1), megabat bufavirus (BAU69605.1), minute virus of mice (NP_041244.1), canine parvovirus (NP_041400.1) and porcine parvovirus (NP_757371.1). Clusters of basic amino acids and some highly conserved R and K are presented within a red frame.