Retroviruses can be engineered to deliver up to 8000 bases of single-stranded RNA, making this the correct answer among the options. This capacity is key for their use in gene therapy vectors.

Question Breakdown

Retroviruses are enveloped RNA viruses with a natural genome of about 7-12 kb, but engineered versions (like lentiviral vectors) have a packaging limit around 8 kb for therapeutic RNA cargo.

Option Analysis

• 500 bases: Too small; this fits microRNAs or tiny regulatory elements, not retroviral vectors which handle full genes.​

• 1000 bases: Still insufficient for most transgenes; adenoviral or AAV vectors might manage this, but retroviruses exceed it.​

• 3000 bases: Approaches some smaller genes but falls short of retrovirus capacity, which supports larger inserts reliably.​

• 8000 bases: Correct; matches the standard limit for retroviral/lentiviral packaging of single-stranded RNA in gene delivery.

Retroviruses in Gene Therapy

Retroviruses reverse-transcribe their single-stranded RNA into DNA for host genome integration, ideal for stable expression. Engineered forms delete viral genes to fit ~8 kb foreign RNA, enabling treatments like CAR-T cells.

Retroviruses deliver 8000 bases RNA in engineered forms, a key fact for GATE Life Sciences exams. These enveloped viruses package up to 8 kb of single-stranded RNA, vital for gene therapy vectors like lentiviruses.​

Retrovirus RNA Packaging Basics

Retroviruses carry two copies of positive-sense single-stranded RNA (~7-12 kb naturally). Engineering removes gag/pol/env genes, freeing ~8 kb for transgenes via reverse transcription and integration.

Capacity stems from virion structure: RNA binds Gag polyprotein, limited by capsid size. Beyond 8-10 kb, efficiency drops sharply.​

Why 8000 Bases?

This limit balances payload with packaging signals (ψ sequence). Studies confirm lentiviral vectors handle 8 kb reliably for clinical use.

For GATE prep, note: smaller options (500-3000 bases) suit non-integrating vectors like AAV (~4.7 kb DNA).​

Exam Relevance

From CUET PG Life Sciences 2024 PYQ: Option 4 (8000 bases) is correct. Memorize for virology sections in GATE XL.​