The mosquito-borne Zika virus (ZIKV) is one of the most feared viruses for pregnant women. Recent statistics justify this fear: Infants born to mothers infected with ZIKV during pregnancy face a risk of up to 42 percent of developing birth defects, including microcephaly (an abnormally small head and decreased brain volume).
What do we know about how ZIKV causes damage to the developing brain?
Draw a model to illustrate how the Zika virus genome is used to produce new virions. In your drawing, identify the steps required to replicate the genome and those used to produce mRNA.
Also note where mRNAs that are used to produce capsid and envelope proteins are translated.

Verified step by step guidance

1. Step 1: Understand the Zika virus structure. Zika virus is an RNA virus, meaning its genetic material is RNA rather than DNA. The virus has a single-stranded positive-sense RNA genome, which means it can be directly translated into proteins by the host cell's ribosomes.
2. Step 2: Entry and uncoating. The Zika virus enters the host cell through receptor-mediated endocytosis. Once inside, the viral envelope fuses with the endosomal membrane, releasing the RNA genome into the cytoplasm.
3. Step 3: Translation of viral proteins. The positive-sense RNA genome is immediately translated by the host cell's ribosomes to produce viral proteins. These include non-structural proteins necessary for replication and structural proteins like capsid and envelope proteins. The mRNAs for capsid and envelope proteins are translated in the rough endoplasmic reticulum.
4. Step 4: Replication of the viral genome. The viral RNA-dependent RNA polymerase, one of the non-structural proteins, synthesizes a complementary negative-sense RNA strand. This strand serves as a template for the production of new positive-sense RNA genomes.
5. Step 5: Assembly and release of new virions. Newly synthesized viral RNA genomes are packaged with capsid proteins to form new virions. These virions acquire their envelope as they bud from the host cell, ready to infect new cells.

Key Concepts

Zika Virus Structure and Genome

The Zika virus is an RNA virus belonging to the Flavivirus genus. Its genome is a single-stranded positive-sense RNA, which means it can be directly translated into proteins by the host cell's ribosomes. Understanding the structure of the Zika virus genome is crucial for identifying how it replicates and produces viral proteins necessary for new virion assembly.

Viral Replication Process

Viral replication involves several key steps: attachment, entry, uncoating, replication, assembly, and release. For Zika virus, replication begins with the synthesis of a complementary negative-sense RNA strand, which serves as a template for producing new positive-sense RNA genomes. This process is essential for generating the genetic material needed for new virions and involves both replication of the genome and transcription of mRNA.

Translation of Viral Proteins

Translation of viral proteins occurs in the host cell's cytoplasm, where mRNAs derived from the viral genome are translated by ribosomes. For Zika virus, specific mRNAs are responsible for producing structural proteins like capsid and envelope proteins, which are crucial for virion assembly. Understanding where and how these proteins are synthesized helps elucidate the virus's lifecycle and its ability to infect new cells.