Rubella virus

Rubella virus ( Rubella virus) is the causative agent of rubella, and is infectious in the first gestational weeks, the cause of congenital rubella syndrome. Man is the only known host of the transmissible by droplet infection virus.

The rubella virus is the only member of the Rubivirus genus belonging to the family Togaviridae, the members will typically have a single stranded RNA genome of positive polarity than that is surrounded by an icosahedral capsid. The RNA genome within the capsid has a length of about 9'757 nucleotides and coding for two non- structural proteins, as well as three structural proteins. The capsid protein and the two envelope proteins E1 and E2 represent the three structural proteins.

The molecular basis for the cause of congenital rubella syndrome is not fully understood, but in vitro studies with cell lines showed that the rubella virus has an apoptotic effect on several cell types. There is evidence of a p53 -dependent mechanism.

Morphology

The spherical particles of the virus Togaviridae having a diameter of 50 to 70 nm and are surrounded by a lipid membrane ( the viral envelope ). In the envelope as distinct spikes ( protrusions ) are incorporated by 6 nm height, the heterodimers of the two viral envelope proteins E1 and E2. Inside the lipid envelope there is an approximately 40 -nm capsid.

Replication

Togaviruses attach to via specific receptors on the cell surface and are taken up by a ausbildendes to Endosomvesikel. At neutral pH outside the cell, the E2 envelope protein covering the E1 protein. Inside the endosome, the outer domains of the E1 protein are exposed now at acidic pH and the fusion of the viral envelope and endosome membrane is induced. Thus, the capsid reaches the cytosol, decays and releases the genome freely. The ( ) ssRNA ( single-stranded positive RNA ) is used only initially of the translation of the nonstructural proteins are synthesized as large polyprotein and subsequently cut into individual proteins. The sequences for the structural proteins are only a complementary - reproduced ssRNA as a template by the viral RNA polymerase ( replicase ) and translated as separate short (mRNA ). This short ( subgenomic ) mRNA is also packaged into the virion.

Wherein translation of the structural proteins is also produced a long polypeptide (110 kDa), that has to be cut into three pieces. Here, the polyprotein is endoproteolytically split into proteins E1, E2 and capsid protein. Wherein E1 and E2 are type I transmembrane proteins which translocation into the endoplasmic reticulum (ER) is done with an N-terminal signal sequence. From the ER to the present as a heterodimer E1 · E2 complex enters the Golgi apparatus, where budding ( budding ) of new virions takes place ( in contrast to the Alpha viruses whose budding on the plasma membrane takes place). The capsid proteins, however, remain in the cytoplasm and attach to the genomic RNA, which they eventually form the capsid.

Capsid protein

The capsid protein (including protein C) has several functions. The main functions are the formation of homo-oligomers in order to form the capsid, and the binding of the genomic RNA. Furthermore, it is responsible for the aggregation of the RNA in the capsid to interact with the membrane proteins E1 and E2, and binds to the human host protein p32, this interaction is essential for the replication of the virus in the host. In contrast to the capsid alphaviruses makes no autoprotolysis, but is separated from the signal peptidase of the rest of the polyprotein. The production of the capsid is made at the surface of the intracellular membranes, at the same time with the budding of virus.