Final answer:
The yeast Ty virus-like particle lacks the envelope protein necessary for infection, separating it from retroviruses and limiting it to retrotransposition within the same cell.
Step-by-step explanation:
The yeast Ty virus-like particle is missing the envelope protein, which is analogous to the ENV protein in retroviruses that facilitates the attachment to host cells and entry into them. While the Ty element encodes for reverse transcriptase and integrase, among other proteins, it does not produce the envelope protein seen in retroviruses. This lack of an envelope protein means that the virus-like particles formed by the Ty element cannot infect new cells like true retroviruses do. Instead, these particles carry out retrotransposition within the same cell, a notable distinction from the infection process of retroviruses.