Final answer:
The uniquely encoded protein by non-LTR retroposons is reverse transcriptase, essential for replicating the retrotransposon within the genome.
Step-by-step explanation:
The protein uniquely encoded by non-LTR retroposons is reverse transcriptase. Non-LTR retrotransposons, such as LINES (Long Interspersed Nuclear Elements), encode enzymes necessary for their transposition. They lack long terminal repeats (LTRs), which are characteristic of LTR retrotransposons and retroviruses. A non-LTR retrotransposon, specifically the LINEs, includes ORFs (open reading frames) with a reverse transcriptase that is essential for the reverse transcription of the RNA into cDNA during the transposition process. It is this reverse transcriptase that permits the retrotransposon to replicate within the genome without the need for an intermediate viral particle, distinguishing it from the mechanisms observed in retroviral infection.