Bacteriophage MS2

File:MS2 phage gene map.svg

The [https://www.ncbi.nlm.nih.gov/nuccore/176120924?report=genbank MS2 genome] is one of the smallest known, consisting of 3569 nucleotides of single-stranded RNA. It encodes just four proteins: the maturation protein (A-protein), the lysis (lys) protein, the coat protein (cp), and the replicase (rep) protein. The gene encoding lys overlaps both the 3'-end of the upstream gene (cp) and the 5'-end of the downstream gene (rep), and was one of the first known examples of overlapping genes. The positive-stranded RNA genome serves as a messenger RNA, and is translated upon viral uncoating within the host cell. Although the four proteins are encoded by the same messenger/viral RNA, they are not all expressed at the same levels.

File:Leviviridae virion.png

An MS2 virion (viral particle) is about 27 nm in diameter, as determined by electron microscopy.{{cite journal | vauthors = Strauss JH, Sinsheimer RL | title = Purification and properties of bacteriophage MS2 and of its ribonucleic acid | journal = Journal of Molecular Biology | volume = 7 | pages = 43–54 | date = July 1963 | pmid = 13978804 | doi = 10.1016/S0022-2836(63)80017-0 }} It consists of one copy of the maturation protein and 180 copies of the coat protein (organized as 90 dimers) arranged into an icosahedral shell with triangulation number T=3, protecting the genomic RNA inside.{{cite journal | vauthors = Valegård K, Liljas L, Fridborg K, Unge T | title = The three-dimensional structure of the bacterial virus MS2 | journal = Nature | volume = 345 | issue = 6270 | pages = 36–41 | date = May 1990 | pmid = 2330049 | doi = 10.1038/345036a0 | bibcode = 1990Natur.345...36V | s2cid = 2803228 }} The virion has an isoelectric point (pI) of 3.9.{{cite journal | vauthors = Dowd SE, Pillai SD, Wang S, Corapcioglu MY |title=Delineating the Specific Influence of Virus Isoelectric Point and Size on Virus Adsorption and Transport Through Sandy Soils |journal=Appl. Environ. Microbiol. |volume=64 |issue=2 |year=1998 |pages=405–410 |doi= 10.1128/aem.64.2.405-410.1998|pmid=9464373 |doi-access=free |pmc=106058 |bibcode=1998ApEnM..64..405D }}

The structure of the coat protein is a five-stranded β-sheet with two α-helices and a hairpin. When the capsid is assembled, the helices and hairpin face the exterior of the particle, while the β-sheet faces the interior.{{cite journal | vauthors = Golmohammadi R, Valegård K, Fridborg K, Liljas L | title = The refined structure of bacteriophage MS2 at 2.8 A resolution | journal = Journal of Molecular Biology | volume = 234 | issue = 3 | pages = 620–39 | date = December 1993 | pmid = 8254664 | doi = 10.1006/jmbi.1993.1616 }}

MS2 infects enteric bacteria carrying the fertility (F) factor, a plasmid that allows cells to serve as DNA donors in bacterial conjugation. Genes on the F plasmid specifies the proteins of the F pilus, which includes the F-pilin protein that serves as the viral receptor. MS2 attaches to the F-pilin on the side of the pilus using its single maturation protein.

Once the viral RNA has entered the cell, it begins to function as a messenger RNA for the production of phage proteins. The gene for the most abundant protein, the coat protein, can be immediately translated. The translation start of the replicase gene is normally hidden within RNA secondary structure, but can be transiently opened as ribosomes pass through the coat protein gene. Replicase translation is also shut down once large amounts of coat protein have been made; coat protein dimers bind and stabilize the RNA "operator hairpin", blocking the replicase start. The start of the maturation protein gene is accessible in RNA being replicated but hidden within RNA secondary structure in the completed MS2 RNA; this ensures translation of only a very few copies of maturation protein per RNA. Finally, the lysis protein gene can only be initiated by ribosomes that have completed translation of the coat protein gene and "slip back" to the start of the lysis protein gene, at about a 5% frequency.

File:1-s2.0-S0022283615006762-gr1-C.jpg

Replication of the plus-strand MS2 genome requires synthesis of the complementary minus strand RNA, which can then be used as a template for synthesis of a new plus strand RNA. MS2 replication has been much less well studied than replication of the highly related bacteriophage Qβ, partly because the MS2 replicase has been difficult to isolate, but is likely to be similar.

The formation of the virion is thought to be initiated by binding of maturation protein to the MS2 RNA;{{cite journal | vauthors = Johansson HE, Liljas L, Uhlenbeck OC | title = RNA Recognition by the MS2 Phage Coat Protein | journal = Seminars in Virology | volume = 8 | issue = 3 | pages = 176–85 | date = December 1997 | doi = 10.1006/smvy.1997.0120 }} in fact, the complex of maturation protein and RNA is infectious. The assembly of the icosahedral shell or capsid from coat proteins can occur in the absence of RNA; however, capsid assembly is nucleated by coat protein dimer binding to the operator hairpin, and assembly occurs at much lower concentrations of coat protein when MS2 RNA is present.

Bacterial lysis and release of newly formed virions occurs when sufficient lysis protein has accumulated. Lysis (L) protein forms pores in the cytoplasmic membrane, which leads to loss of membrane potential and breakdown of the cell wall. The lysis protein is known to bind to DnaJ via an important P330 residue.{{cite journal | vauthors = Chamakura KR, Tran JS, Young R | title = MS2 Lysis of Escherichia coli Depends on Host Chaperone DnaJ | journal = Journal of Bacteriology | volume = 199 | issue = 12 | date = June 2017 | pmid = 28396351 | pmc = 5446614 | doi = 10.1128/JB.00058-17 }} A LS dipeptide motif on the L protein is found throughout the genus Levivirus and appears to be essential to the lysis activity, although their different locations suggest that they have evolved independently.{{cite journal | vauthors = Chamakura KR, Edwards GB, Young R | title = Mutational analysis of the MS2 lysis protein L | journal = Microbiology | volume = 163 | issue = 7 | pages = 961–969 | date = July 2017 | pmid = 28691656 | pmc = 5775895 | doi = 10.1099/mic.0.000485 | doi-access = free }}

In 1961, MS2 was isolated by Alvin John Clark and recognized as an RNA-containing phage very similar to bacteriophage f2.{{cite journal | title = National Academy of Sciences: Abstracts of Papers Presented at the Autumn Meeting, 29 October, La Jolla, California, 30 October-1 November 1961, Los Angeles | journal = Science | volume = 134 | issue = 3488 | pages = 1425–37 | date = November 1961 | pmid = 17795773 | doi = 10.1126/science.134.3488.1425 | bibcode = 1961Sci...134.1425. }}

In 1976, the MS2 genome was the first genome to be completely sequenced.{{cite journal | vauthors = Fiers W, Contreras R, Duerinck F, Haegeman G, Iserentant D, Merregaert J, Min Jou W, Molemans F, Raeymaekers A, Van den Berghe A, Volckaert G, Ysebaert M | title = Complete nucleotide sequence of bacteriophage MS2 RNA: primary and secondary structure of the replicase gene | journal = Nature | volume = 260 | issue = 5551 | pages = 500–7 | date = April 1976 | pmid = 1264203 | doi = 10.1038/260500a0 | bibcode = 1976Natur.260..500F | s2cid = 4289674 }} This was accomplished by Walter Fiers and his team, building upon their earlier milestone in 1972 of the first gene to be completely sequenced, the MS2 coat protein.{{cite journal | vauthors = Min Jou W, Haegeman G, Ysebaert M, Fiers W | title = Nucleotide sequence of the gene coding for the bacteriophage MS2 coat protein | journal = Nature | volume = 237 | issue = 5350 | pages = 82–8 | date = May 1972 | pmid = 4555447 | doi = 10.1038/237082a0 | bibcode = 1972Natur.237...82J | s2cid = 4153893 }} These sequences were determined at the RNA level.{{cite journal | vauthors = Sanger F, Air GM, Barrell BG, Brown NL, Coulson AR, Fiddes CA, Hutchison CA, Slocombe PM, Smith M | title = Nucleotide sequence of bacteriophage phi X174 DNA | journal = Nature | volume = 265 | issue = 5596 | pages = 687–95 | date = February 1977 | pmid = 870828 | doi = 10.1038/265687a0 | bibcode = 1977Natur.265..687S | s2cid = 4206886 }}

The first effort at a statistical analysis of the MS2 genome was a search for patterns in the nucleotide sequence. Several non-coding sequences were identified, however at the time of this investigation (1979), the functions of the non-coding patterns were unknown.{{cite journal | vauthors = Erickson JW, Altman GG | title = A search for patterns in the nucleotide sequence of the MS2 genome. | journal = Journal of Mathematical Biology | date = April 1979 | volume = 7 | issue = 3 | pages = 219–30 | doi = 10.1007/BF00275725 | s2cid = 85199492 }}

Since 1998,{{cite journal | vauthors = Bertrand E, Chartrand P, Schaefer M, Shenoy SM, Singer RH, Long RM | title = Localization of ASH1 mRNA particles in living yeast | journal = Molecular Cell | volume = 2 | issue = 4 | pages = 437–45 | date = October 1998 | pmid = 9809065 | doi = 10.1016/S1097-2765(00)80143-4 | doi-access = free }} the MS2 operator hairpin and coat protein have found utility in the detection of RNA in living cells (see MS2 tagging). MS2 and other viral capsids are also currently under investigation as agents in drug delivery, tumor imaging, and light harvesting applications.{{cite journal | vauthors = Glasgow J, Tullman-Ercek D | title = Production and applications of engineered viral capsids | journal = Applied Microbiology and Biotechnology | volume = 98 | issue = 13 | pages = 5847–58 | date = July 2014 | pmid = 24816622 | doi = 10.1007/s00253-014-5787-3 | s2cid = 6212583 }}

MS2, due to its structural similarities to noroviruses, its similar optimum proliferation conditions, and non-pathogenicity to humans, has been used as substitute for noroviruses in studies of disease transmission.{{cite web|url=http://www.today.com/health/viruses-spread-crazy-office-1D80134085|title=Viruses spread 'like crazy' in an office, study finds| first = Maggie | last = Fox | work = The Today Show | date = 8 September 2014 }}

{{Portal|Viruses}}

• bacteriophage
• bacteriophage f2
• bacteriophage Qβ
• phi-X174 phage
• MS2_tagging

{{Reflist|2}}

• [https://www.ncbi.nlm.nih.gov/nuccore/EF204940.1 Complete genome] (also isolates [https://www.ncbi.nlm.nih.gov/nuccore/EF108465.1 R17], [https://www.ncbi.nlm.nih.gov/nuccore/EF108464.1 DL16], and [https://www.ncbi.nlm.nih.gov/nuccore/EF204939.1 J20])

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{{DEFAULTSORT:Bacteriophage Ms2}}

Category:Bacteriophages

Category:Fiersviridae