Positive sense nucleic acid genome is found in –
**Core Concept**
Positive sense nucleic acid genomes are a type of RNA or DNA that can directly act as messenger RNA (mRNA) to translate into proteins, unlike negative sense nucleic acid genomes which require a complementary RNA transcript to be synthesized first. This characteristic is crucial in the replication and transcription of viruses that possess positive sense nucleic acid genomes.
**Why the Correct Answer is Right**
Positive sense nucleic acid genomes are typically found in RNA viruses such as coronaviruses, flaviviruses, and picornaviruses. These viruses can directly translate their positive sense RNA into proteins, allowing them to replicate and produce new viral particles rapidly. The presence of a cap structure at the 5' end of the RNA and a poly-A tail at the 3' end also contributes to the stability and translation efficiency of positive sense RNA genomes.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because negative sense nucleic acid genomes, found in viruses such as influenza and rabies, require a complementary RNA transcript to be synthesized before translation can occur.
**Option B:** This option is incorrect because DNA viruses, such as herpesviruses and adenoviruses, possess double-stranded DNA genomes that are replicated through a process involving DNA polymerase.
**Option C:** This option is incorrect because retroviruses, such as HIV, possess a positive sense RNA genome that is first converted into double-stranded DNA through a process involving reverse transcription.
**Clinical Pearl / High-Yield Fact**
It's essential to note that the distinction between positive and negative sense nucleic acid genomes is crucial in understanding the replication and transcription strategies employed by different viruses, which in turn informs antiviral therapy and vaccine development.
**Correct Answer: A. RNA viruses.**