Can PolyA tails be within Expressed Sequence Tags?
The CATGTC sequence at the end of the poly A tail is an artefact of the method used in constructing the original cDNA library.

According to https://www.ncbi.nlm.nih.gov/nucest/EE485195.1 this EST comes from a library constructed in the Clontech vector pDNR-LIB

The Clontech SMART cDNA cloning system manuals are linked to from here
and the general manual descibes the use of a primer for 1st strand synthesis:


  CDS III/3' PCR Primer  5'-ATTCTAGAGGCCGAGGCGGCCGACATG-d(T)30N-1N-3'
  
  (N = A, G, C, or T; N-1 = A, G, or C)


If you look carefully at the primer you will see that the oligo dT portion, designed to anneal to the poly-A tail of the mRNA is preceded by the sequence GACATG and a SfiI site that is used in some clever cloning strategy that I don't fully understand. What is clear however is that the use of this primer will put CATGTC immediately after the poly A in the cDNA:

           .....SfiI....
5'-ATTCTAGAGGCCGAGGCGGCCGACATGTTTTTTTTTTTTTTTTTTT...
   TAAGATCTCCGGCTCCGCCGGCTGTACAAAAAAAAAAAAAAAAAAA...5'

&gt;&gt;&gt; turning bottom strand around -  5' ...AAAAAAACATGTC