A role for transportin in the nuclear import of Adenovirus core proteins and dna

The research paper of Hindley and colleagues (2007) describes the function of the protein transportin in the entry of adenovirus-associated proteins in a cell.  Adenoviruses are microbial organisms that contain genetic material that has been highly compacted by the help of adenoviral core proteins.

The DNA packaging facilitators have been known as terminal proteins and three types have been characterized by previous studies (Robinson et al., 1979).  It has been determined that these terminal proteins exist as two units, each one associates with the 5’ end of the DNA strand.  One of the terminal proteins, called protein VII, is created by the deletion of the terminal 24 resides of the precursor polypeptide preVII.

The precursor protein, composed of 197 amino acid residues, is produced by the protease enzyme of the adenovirus right after the generation of new viral microorganisms.  It has been determined that the processed protein VII makes up most of the core protein content of an adenovirus and it situated in close proximity to the DNA strand of an adenovirus.  Another core protein that is present in significant amounts in an adenovirus is protein V.

This 369-residue polypeptide has been postulated to link the core to the adenoviral coat.  The third core protein, termed Mu, also shows the ability of package viral DNA.

Previous research has shown that the core proteins V and VII have the capacity to send signals that would dictate importation of material into the nucleus as well as compaction of nucleolar material (Wodrich et al., 2006).  However, the authors of the research article were aware that there has been no research effort conducted in order to determine the relation of these two terminal coreproteins and the process of importation of materials into the nucleus.

The proponents of this research paper then set off to investigate the specific associations that between the import signals and the terminal core proteins.  In order to examine this relationship, the proponents of the research extracted the import receptors that were involved in the viral import process.  Isolated terminal core proteins were also prepared.

A cell import experimental setup was developed in order to test each import receptor against each of the terminal core proteins.  The receptors were introduced to an established cancer cell line (HeLa) in order to determine whether any association will take place.  Simple import routes were also tested using the protein importin, which has the ability to associated core proteins.

Both precursor and mature core proteins were tested in order to determine the temporal interactions that occur within an adenovirus.  In order to compare the action of other binding proteins with the core proteins, the protein transportin was also employed in the binding assay.  Pull-down assays were also conducted in order to catch a glimpse of the actual protein-protein associations within particular stages of the adenoviral cycle.

The assays showed that the binding protein transportin was necessary for the success of core protein V to attach to the nucleolar material of the adenovirus.  This result suggested that the packaging of nucleolar material can not be triggered by any type of binding protein but by a specific one such as transportin.

The pull-down assays also showed that precursor and mature core proteins behaved differently within an adenoviral organism.  This observation provides an explanation why a significant number of amino acid residues have to be deleted from the precursor protein preVII.  The truncation actually does not only make the polypeptide shorter but specifically helps in the identification of particular signal motifs that would trigger further packaging of genetic material within an adenovirus.