In insects, does the Alanine repeat occur on the homeodomain sequence of the abdomen or does it occur on a different sequence?
Some background:


  The new work involved misexpression of the Drosophila Ubx protein in the presumptive thorax of transgenic fruitfly embryos. Limb development was suppressed because of repression of Dll. By contrast, the misexpression of onychophoran and crustacean Ubx proteins did not interfere with Dll expression and the formation of thoracic limbs. These results raised the possibility that the Drosophila Ubx protein is functionally distinct from Ubx in onychophorans and crustaceans. One study suggests that Drosophila Ubx has acquired an alanine-rich peptide that mediates the repression of gene transcription; this peptide is lacking in onychophorans. The other study provides evidence that the crustacean Ubx contains an additional peptide that modulates the activity of the alanine-rich peptide, and possibly other repression domains, in crustacean Ubx.





  Insect-restricted sequences include four regions N-terminal to the
  homeodomain (I1–I4), a peptide motif (QAQAQK), and an extended run of
  alanine residues C-terminal to the homeodomain
  
  The onychophoran Ubx protein might function as an activator of appendage development. When the onychophorans and arthropods diverged,
  Ubx acquired an alanine-rich repression domain near its carboxy
  terminus. This domain mediates constitutive repression in insects.
  But in crustaceans the addition of the regulatory peptide causes it to
  function in a conditional fashion. As a result, Ubx does not suppress
  limb development in crustaceans. But it eliminates abdominal limbs in
  insects, greatly reducing the overall number of appendages compared
  with crustaceans.


You can read about it here: 

Levine, Mike. "Evolutionary biology: how insects lose their limbs." Nature 415.6874 (2002): 848-849.

Galant, Ron, and Sean B. Carroll. "Evolution of a transcriptional repression domain in an insect Hox protein." Nature 415.6874 (2002): 910-913.