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The "Transactivator/viroplasmin protein" (TAV) -also known as "Inclusion body matrix protein" (IBMP)- is a multifunctional protein encoded by several caulimoviruses such as those belonging to the ''Caulimovirus'', ''Soymovirus'' and ''Cavemovirus'' genera and involved in many aspects of the virus life cycle ([[Literature:100786|Haas ''et al.'' 2005]]; [[Literature:100739|Kobayashi and Hohn, 2003]]; [[Literature:100719|Petrzik ''et al.'' 1998]]; [[Literature:100733|Richins ''et al.'' 1987]]; [[Literature:100707|Hull ''et al.'' 1986]]; [[Literature:100602|Hasegawa ''et al''. 1989]]; [[Literature:100603|Mushegian ''et al'', 1995]]; [[Literature:100686|Glasheen ''et al.'' 2002]];[[Literature:100606|de Kochko ''et al.'' 1998]]; [[Literature:100607|Lockhart ''et al.'' 2000]]).

The ''Cauliflower mosaic virus'' (CaMV)-ORF 6 product (P6) is probably the most extensively studied TAV (see also [[Literature:100780|Covey and Hull 1981]]). In this viral species, TAV has been shown to be essential for basic virus replication ([[Literature:100739|Kobayashi and Hohn, 2003]]) and it is the major component of CaMV inclusion bodies or viroplasm, which are large membrane-free structures (with the size of organelles) where CaMV protein synthesis, reverse transcription and virion assembly occur ([[Literature:100785|Kobayashi and Hohn, 2004]]; [[Literature:100786|Haas ''et al.'' 2005]]). TAV has also been shown to promote the translation of the polycistronic CaMV second major transcript 35S RNA ([[Literature:100787|Hohn ''et al.'' 1990]]) and it is capable to induce hypersensitive response (HR) in some plant hosts ([[Literature:100785|Kobayashi and Hohn, 2004]]). Prior studies demonstrated that CaMV-TAV is the major determinant of host specificity and influences symptom severity ([[Literature:100782|Daubert ''et al.'' 1984]]; [[Literature:100783|Daubert and Routh, 1990]]; [[Literature:100781|Agama ''et al.'' 2002]]), and it has also been suggested to have post-translational roles in virus replication ([[Literature:100739|Kobayashi and Hohn, 2003]]).

TAV has been considered a mosaic of different domains whose function independently and have different properties ([[Literature:100784|De Tapia ''et al.'' 1993]]; [[Literature:100739|Kobayashi and Hohn 2003]]; [[Literature:100785|2004]]). The figure below shows a schematic representation of TAV domain architecture. Based on Kobayashi and Hohn ([[Literature:100739|2003]]; [[Literature:100785|2004]]) four domains (I, II, III, IV) can be distinguished in TAV. Domains I and IV include two hypervariable regions (HVRs 1-2) that appear to be responsible for host selection and/or pathogenesis. Domain I contains the region required for CaMV virulence and avirulence (Vi/Av) and plays also role in viroplasm formation. Domains II and III contain the "caulimoblock" a preserved region between amino acids (aa) 283 and 350 ([[Literature:100784|De Tapia ''et al.'' 1993]]) that probably play a role in basic virus replication. Domain II includes the "Mini-TAV", a small portion of protein containing the active center (AC) of TAV which interacts with ribosomal protein L18, double-stranded RNA (dsRNA) and RNA–DNA hybrids ([[Literature:100739|Kobayashi and Hohn, 2003]]; [[Literature:100800|Cerritelli ''et al.'' 1998]]). Domain III is a multifunctional region that includes a multiple binding domain (MBD or RBa; aa 242 to 310) with affinity for both protein and RNA; a second RNA domain (RB-b; aa 346 to 378) as well as an interactive domain (ID) proposed from the competition experiments for transactivation activity ([[Literature:100784|De Tapia'' et al.'' 1993]]; [[Literature:100739|Kobayashi and Hohn, 2003]]).

<center>[[File:TAV.png]]</center>

<center>'''CaMV-TAV domain map'''</center>

[[Category:Retroelements]]

Translational transactivator Protein - Revision history

imported>Gydbwiki at 10:25, 22 April 2010