Hi Aydin,

It is a good question. If you look at the proteins encoded by late genes it will give the answer. In general, most of the late genes encodes proteins that are required for viral assembly and nuclear egress. Hence, logically we can conclude that expression of certain viral proteins which function as regulators (viral trans factors) are required for expression of late genes. Further, there are some suggestions for replication associated modifications in DNA such methylation pattern also. Please search for original articles based on these concepts.

Thank you dear Narayanan;

I will take into account your suggestions. But, I was not wondering that the late expressed proteins which are required for DNA replication. My main question is, how is possible that when DNA repl. was inhibited, late genes cannot be transcribed? What is the relationship between new synthesized DNA and initiation of late gene transcription?

Hi Aydin,

You can observe this phenomena mainly in retroviruses and DNA viruses that require integration of genomic material into the host cell. The primary reason is the transcription of viral proteins solely depends on the host machinery. Hence, establishment of an infection is more critical than viral replication. Thus, if we inhibits viral replication at the early phase of an infection we can contain the infection. That's why we provide drugs to inhibit viral entry and viral replication. The activation signals that required for expression of late genes is often linked with a set of operon(s).

Theoretically, expression of operon itself contained thereby expression of late genes also contained. There is a threshold for release of viral progeny to infect new cells. The proteins encoded by late genes were often related with release of viral progeny not for establishment of an infecion (at early phase). Hence, inhibition of viral replication certainly switch-off the expression of late genes until the threshold for release of viral progeny or newer virus to infect further or bystander cells. I understand that the inhibition of late gene expression (via natural process) provide sufficient time to establish infection via evasion of host immune response. The remnants of proteins expressed by late gene also enhances the probability for detection of host immune machinery. I think the fine balance between the survival strategy of the virus and host leads to evolution of late gene expression under stringent regulation

@Narayanan Kalyaranaman I've really thankful for these explanations.

Best wishes