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9.B.308.  The Lettuce Infectious Yellows Virus P5 (LIYV-P5) Family 

The LIYV P5 protein is 39 aas long and has 1 TMS. It is part of the conserved quintuple gene block in the family Closteroviridae. The LIYV P5 protein is an endoplasmic reticulum (ER)-localized integral transmembrane protein. The knockout LIYV mutant presented reduced symptom severity and virus accumulation in Nicotiana benthamiana or lettuce plants, indicating its importance in efficient virus infection. P5, as well as its ortholog P6, encoded by Citrus tristeza virus (CTV) and another ER-localized protein encoded by LIYV RNA1, were found to cause cell death when expressed in N. benthamiana plants from a TMV vector, and it induced ER stress as well as the unfolded protein response (UPR) (Qiao et al. 2018). Several putative orthologues in different viruses are mentioned by Qiao et al. 2018, and these are presented in this family, although most of them show minimal sequence similarity.

References associated with 9.B.308 family:

Cowan, G.H., F. Lioliopoulou, A. Ziegler, and L. Torrance. (2002). Subcellular localisation, protein interactions, and RNA binding of Potato mop-top virus triple gene block proteins. Virology 298: 106-115. 12093178
Haupt, S., G.H. Cowan, A. Ziegler, A.G. Roberts, K.J. Oparka, and L. Torrance. (2005). Two plant-viral movement proteins traffic in the endocytic recycling pathway. Plant Cell 17: 164-181. 15608333
Peremyslov, V.V., Y.W. Pan, and V.V. Dolja. (2004). Movement protein of a closterovirus is a type III integral transmembrane protein localized to the endoplasmic reticulum. J. Virol. 78: 3704-3709. 15016890
Qiao, W., E.L. Helpio, and B.W. Falk. (2018). Two Crinivirus-Conserved Small Proteins, P5 and P9, Are Indispensable for Efficient Infectivity in Plants. Viruses 10:. 30154314
Shemyakina, E.A., A.G. Solovyev, O.G. Leonova, V.I. Popenko, J. Schiemann, and S.Y. Morozov. (2011). The Role of Microtubule Association in Plasmodesmal Targeting of Potato mop-top virus Movement Protein TGBp1. Open Virol J 5: 1-11. 21660184
Tilsner, J., G.H. Cowan, A.G. Roberts, S.N. Chapman, A. Ziegler, E. Savenkov, and L. Torrance. (2010). Plasmodesmal targeting and intercellular movement of potato mop-top pomovirus is mediated by a membrane anchored tyrosine-based motif on the lumenal side of the endoplasmic reticulum and the C-terminal transmembrane domain in the TGB3 movement protein. Virology 402: 41-51. 20350737
Zamyatnin, A.A., Jr, A.G. Solovyev, E.I. Savenkov, A. Germundsson, M. Sandgren, J.P. Valkonen, and S.Y. Morozov. (2004). Transient coexpression of individual genes encoded by the triple gene block of potato mop-top virus reveals requirements for TGBp1 trafficking. Mol. Plant Microbe Interact. 17: 921-930. 15305613