Question

After the fusion of the viral and endosomal membranes, the negative-stranded genome segments of influenza virus are released into the cytoplasm. Describe what happens to genome segments 4, 5 and 7 during the viral replication cycle (see slides 21 and 28 of lecture 32 Powerpoint presentation). You descriptions should include:

• Where they are localized
• How the gene products they encode are expressed, including all viral and cellular proteins that are involved
• How each of the gene products encoded by each segment are trafficked through the infected cell, including each of the cellular compartments involved in the trafficking
• Where each of the gene products end up in the progeny virions

Provide a separate description for each of the genome segments (even though some of the steps are the same for each). Your descriptions should be concise but should include all relevant details.

Genome segment 4:

Genome segment 5:

Genome segment 7

Answer 1

After the fusion of the viral and endosomal membranes, the negative-stranded genome segments of influenza virus are released into the cytoplasm. There are eight gene segments that make up the negative single-stranded RNA of the Influenza A virus. The gene segments are known as PB1, PB2, PA, NP, HA, NA, M, and NS. This virus is capable of packaging their segmented genomes into the progeny virions. Such packaging signals of influenza virus RNAs are located in the 5′ and 3′ noncoding regions and in the terminal regions. To find out the roles of the seven segments during influenza A virus genome assembly, HEF virus was taken to examine the effects of replacing the packaging sequences of other segments with those of the NA segment. There was no effect on the growth of the HEF virus by removing the packaging signals of the PB1, HA, or NS segment but growth was affected when the packaging sequence of the PB2, PA, nucleoprotein (NP), or matrix (M) segment was removed. This means that the PB2, PA, NP, and M segments are more important than the remaining four vRNAs during the genome-packaging process.

Influenza virus possess an envelope membrane, inside which a layer of matrix protein 1 (M1) and the core viral ribonucleoprotein (vRNP) complexes, which are made of viral RNAs (vRNAs) and the binding proteins. These binding proteins are heterotrimeric polymerase and multiple copies of nucleoprotein (NP). These vRNPs are transported into the nucleus and they will perform transcription and replication. Due to this multisegmented nature, influenza A virus assembles all its genomic segments together at the same time. During influenza A virus genome packaging, the four segments PB2, PA, NP and M interact in the packaging signal regions, thus making the PB1, HA, NA, and NS segments to join and form the 7 + 1 vRNP complex. The M gene is the seventh segment and it encodes the M1 (matrix protein) and M2 (membrane) proteins. The matrix protein is located beneath the lipid membrane and its function is to give support and strength to the viral envelope. The M2 transmembrane protein is an ion channel which will uncover the virus once it is inside the host cell. With the help of M1 and NP proteins together, we can easily find whether the influenza virus is type A, B, or C.