Final Answer:
The transposase is encoded by sequence located only within the LTRs = long terminal repeats.
Step-by-step explanation:
Transposons, also known as transposable elements (TEs), are DNA sequences that can change their position within a genome. The transposase enzyme is responsible for the movement of these elements. In the case of retrotransposons, which have long terminal repeats (LTRs), the transposase is encoded within these repeats.
LTRs are identical sequences found at both ends of retrotransposons, and they play a crucial role in the transposition process. The transposase coding sequence is embedded within the LTRs, and it is transcribed along with the rest of the retrotransposon. This transcript is then translated into the transposase enzyme, which facilitates the movement of the retrotransposon to a new location in the genome.
Contrary to the option "On the outside of direct repeats" or "Downstream from the recipient target sequence," the correct location for the transposase encoding sequence is specifically within the LTRs. This arrangement is essential for the proper functioning of retrotransposons and is a characteristic feature of these elements in the genome.
Understanding the precise location of the transposase coding sequence provides insights into the molecular mechanisms underlying transposition events mediated by retrotransposons.