Identification and characterization of multiple conserved nuclear localization signals within adenovirus E1A

- HAdV E1A uses multiple mechanisms for nuclear import.
- We identified an additional non-canonical NLS in the N-terminal/CR1 portion of E1A.
- The new NLS does not contact importin-alpha directly.
- All NLSs are functionally conserved in the E1A proteins of all 6 HAdV species.

The human adenovirus 5 (HAdV-5) E1A protein has a well defined canonical nuclear localization signal (NLS) located at its C-terminus. We used a genetic assay in the yeast Saccharomyces cerevisiae to demonstrate that the canonical NLS is present and functional in the E1A proteins of each of the six HAdV species. This assay also detects a previously described non-canonical NLS within conserved region 3 and a novel active NLS within the N-terminal/conserved region 1 portion of HAdV-5 E1A. These activities were also present in the E1A proteins of each of the other five HAdV species. These results demonstrate that, despite substantial differences in primary sequence, HAdV E1A proteins are remarkably consistent in that they contain one canonical and two non-canonical NLSs. By utilizing independent mechanisms, these multiple NLSs ensure nuclear localization of E1A in the infected cell.