Final answer:
Without the env gene, yeast retrotransposon Ty is unable to create infectious particles as it cannot produce the envelope protein crucial for the formation and infection process of retroviruses.
Step-by-step explanation:
Because of the yeast retrotransposon Ty's lack of the env gene, it is unable to make infectious particles. The env gene is responsible for encoding the envelope protein that is vital for the formation of infectious retrovirus particles. Ty elements, despite resembling retroviruses in many ways, lack this crucial gene, which results in their inability to form complete and infectious particles that can leave the host cell.
Retroviruses such as HIV, use their envelope proteins to attach to and enter host cells, subsequently releasing viral RNA into the cytoplasm. Reverse transcriptase then converts this RNA into DNA, which integrates into the host genome and produces components for new viral particles. In contrast, Ty elements produce a capsid-like structure with the aid of the Gag protein, but without the env gene, they cannot produce the envelope that allows for cell-to-cell infection. Instead, the resulting virus-like particles (VLPs) remain within the same cell to integrate new copies of the retrotransposon into the yeast genome.