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:
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.
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.
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.
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:.
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.
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.
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.
Examples:
TC#	Name	Organismal Type	Example
9.B.308.1.1	*The P5 protein of 39 aas and 1 N-terminal TMS. It may be capable of forming an oligomeric channel in plant cell membranes, causing ER stress and inducing cell death (Qiao et al.* 2018).**		P5 of Lettuce infectious yellows virus

Examples:
TC#	Name	Organismal Type	Example
9.B.308.2.1	P6 protein of 51 aas and 1 N-terminal TMS.		P6 of the Citrus tristeza virus

Examples:
TC#	Name	Organismal Type	Example
9.B.308.3.1	P6 protein of 56 aas and 1 N-terminal TMS.		P6 protein of the fig mild mottle-associated virus

9.B.308.3.2	ER movement protein p6 (6 kDa protein) (or ORF2) of 54 aas and 1 N-terminal TMS. Cell-to-cell movement of beet yellows closterovirus requires four structural proteins and the 6-kDa protein (p6). Either virus infection or p6 overexpression results in association of p6 with the rough endoplasmic reticulum. The p6 protein has a hydrophilic, C-terminal domain that is localized on the cytoplasmic face of the ER. In the infected cells, p6 forms a disulfide bridge via a cysteine residue located near the protein's N terminus. Mutagenic analyses indicated that each of the p6 domains, as well as protein dimerization, is essential for p6 function in virus movement (Peremyslov et al. 2004).		P6 of beet yellows virus

Examples:
TC#	Name	Organismal Type	Example
9.B.308.4.1	The P4 protein of 37 aas and 1 N-terminal TMS.		P4 protein of Cordyline virus 1

9.B.308.4.2	4.2 kDa transmembrane protein of 35 aas and 1 N-terminal TMS.		Protein of Cordyline virus 2

Examples:
TC#	Name	Organismal Type	Example
9.B.308.5.1	P5 protein of 44 aas and 1 N-terminal TMS.		P5 protein of the Blackberry vein banding-associated viru

Examples:
TC#	Name	Organismal Type	Example
9.B.308.6.1	Three comoponent (triple gene block, TGB) TGBp1, 2 and 3, of 463 and 0 - 2 TMSs; 119 aas with 2 TMSs, N- and C-terminal, and 190 aas with 2 TMSs, N- and C-terminal, respectively, of potato mop-top virus (PMTV) (Cowan et al. 2002; Zamyatnin et al. 2004). This 3-component complex participates in the transport of viral RNA to the plasmodemata (Haupt et al. 2005). TGBp3 most probably contains signals of plasmodesmata targeting and is therefore involved in the targeting of TGBp2 and viral RNAs-TGBp1 (RNP complex), to plasmodesmata (Tilsner et al. 2010). TGBp2 can gate plasmodesmata and increase their size exclusion limit. TGBp2 and TGBp3 are necessary for the intracellular delivery of TGBp1-containing vRNPs to plasmodesmata (Shemyakina et al. 2011). Microtubule association is required for plasmodesmal targeting of TGBp1 (Shemyakina et al. 2011).		PGBp1, PGBp2 and PGBp3 of Potato mop-top virus (isolate Potato/Sweden/Sw) (PMTV)