A polyA tail can be defined as a string of length 10 or greater containing only 'A' or 'N'.

For example,

AAAANAAAAANNNAANANANN

or

AAAAAAAAAAAAAAAANNAAA

The files to search contain 80 character lines terminated with a control-M, as follows :

ACGGAAAATCGGATCTGAATGTCTAGAGGGGTTCTCTCCCTTGGTGTGAGTCTAGCCCTGAAAGTTGCCACTCATTGAGC^M CGTTGCCGACTGAGGCTTTGGACTCCAAGGGTAAGGAGCAGACGATGGAGGACGATTTGCTTTGGGGCATCACGCAACCA^M TCCCACTCTCGCGAAGCCAAATTTGTCGAGAGTACTCTGGGGGGAAGAGATCAGAATTGTGCAGACTAATCCGTAACTGC^M CAAGTACTATTGGCCCTGTTCCAACCATCTAACCTCCTTATGATAACCATGCCACTAAATGGGTTCCTGGATCTGCACCT^M CATTCGCTCGCCTTATGGCCTCGGCTCTCTGCGTATCCACCCTCCTCGTCACCGCCATGCCCTTCGACCTTCAGCGGGGG^M

Thus far, I have used only grep, but I think the control-M may be imbedded in some of the poly A stretches.

Thank you again!