Molecular biology


Enveloped, spherical to pleomorphic in shape, 80-100 nm in diameter.


Monopartite, linear, dimeric, ssRNA(+) genome of about 8-10 kb, with a 5’-cap and a 3’poly-A tail. There are two long terminal repeats (LTRs) of about 600nt long at the 5’ and 3’ ends. The LTRs contain the U3, R, and U5 regions. There are also a primer binding site (PBS) at the 5’end and a polypurine tract (PPT) at the 3’end.


The integrated provirus utilizes the promoter elements in the 5’LTR to drive transcription. This gives rise to the unspliced full length mRNA that will serve as genomic RNA to be packaged into virions or used as a template for translation of gag, gag-pro (1 ribosomal frameshift), and gag-pro-pol (2 ribosomal frameshifts) polyproteins. The spliced mRNAs encode env that is cleaved into SU and TM envelope proteins and sag, a superantigen encoded at the 3’end of the MMTV genome.



  1. Virus attaches to host receptors through the SU glycoprotein. TM glycoprotein mediates fusion with cell membrane.
  2. Internalization and partial uncoating.
  3. ssRNA(+) genome is copied into a linear dsDNA molecule by the reverse transcriptase.
  4. Nuclear entry of the viral dsDNA when the nuclear membrane is disassembled at mitosis.
  5. Viral dsDNA is covalently and randomly integrated into the cell’s genome by the viral integrase (=provirus).
  6. Transcription of provirus by Pol II produces viral spliced and unspliced RNAs.
  7. Nuclear export of the incompletely spliced RNAs.
  8. Translation of unspliced viral RNAs produces Env, Gag and Gag-Pol polyproteins.
  9. Assembly of the virion as intracytoplasmic particles.
  10. Intracytoplasmic particles relocate to the plasma membrane, become enveloped, and are released.
  11. Proteolytic processing of the precursors polyproteins by viral protease and maturation of the virions.

Host-virus interaction


Mouse Mammary Tumour virus expresses a superantigen to evade innate immune response


Matching UniProtKB/Swiss-Prot entries

36 entries grouped by strain (browse by keywords)

All proteins are shown (view only 26 complete proteome entries)

5 entries

Mouse mammary tumor virus (strain C3H) (MMTV) reference strain

Select_all Deselect_all  
ENV_MMTVCEnvelope glycoprotein gp70 (Env polyprotein)
GAG_MMTVCGag polyprotein
POL_MMTVCGag-Pro-Pol polyprotein
PR73_MMTVCProtein PR73 (Superantigen) (Sag)
PRO_MMTVCGag-Pro polyprotein

5 entries

Mouse mammary tumor virus (strain BR6) (MMTV)

Select_all Deselect_all  
ENV_MMTVBEnvelope glycoprotein gp70 (Env polyprotein)
GAG_MMTVBGag polyprotein
POL_MMTVBPol polyprotein
PR73_MMTVBProtein PR73
VPRT_MMTVBProtease (EC 3.4.23.-)

5 entries

Sheep pulmonary adenomatosis virus (Jaagsiekte sheep retrovirus) (JSRV)

Select_all Deselect_all  
ENV_JSRVEnvelope glycoprotein (Env polyprotein)
GAG_JSRVGag polyprotein
POL_JSRVPol polyprotein
VPRT_JSRVBifunctional protease/dUTPase
VPU_JSRVProtein Vpu (ORF-X protein)

4 entries

Mason-Pfizer monkey virus (MPMV) (Simian Mason-Pfizer virus)

Select_all Deselect_all  
ENV_MPMVEnvelope glycoprotein (Env polyprotein)
GAG_MPMVGag polyprotein (Core polyprotein)
POL_MPMVPol polyprotein
VPRT_MPMVProtease (EC 3.4.23.-)

4 entries

Mouse mammary tumor virus (strain GR) (MMTV)

Select_all Deselect_all  
ENV_MMTVGEnvelope glycoprotein gp70 (Env polyprotein)
PR73_MMTVGProtein PR73
PR7L_MMTVGProtein PR73 5'-endogenous
PR7R_MMTVGProtein PR73 3'-endogenous

4 entries

Simian retrovirus SRV-1

Select_all Deselect_all  
ENV_SRV1Envelope glycoprotein (Env polyprotein)
GAG_SRV1Gag polyprotein (Core polyprotein)
POL_SRV1Pol polyprotein
VPRT_SRV1Protease (EC 3.4.23.-)

4 entries

Simian retrovirus SRV-2

Select_all Deselect_all  
ENV_SRV2Envelope glycoprotein (Env polyprotein)
GAG_SRV2Gag polyprotein (Core polyprotein)
POL_SRV2Pol polyprotein
VPRT_SRV2Protease (EC 3.4.23.-)

4 entries

Squirrel monkey retrovirus (SMRV-H) (SMRV-HLB)

Select_all Deselect_all  
ENV_SMRVHEnvelope glycoprotein (Env polyprotein)
GAG_SMRVHGag polyprotein
POL_SMRVHPol polyprotein
VPRT_SMRVHProtease (EC 3.4.23.-)

1 entry

Simian retrovirus SRV-2 (isolate 2R-18B1)

ENV_SRV2REnvelope glycoprotein (Env polyprotein)