I didn't test it, but see if it works: 
([AGCT])(?!\1)([AGCT])(?!\1|\2)([AGCT])(?!\1|\2|\3)[AGCT],([AGCT])(?!\
+4)([AGCT])(?!\4|\5)([AGCT])(?!\4|\5|\6)[AGCT]

[download]
No, it would only do for 4 char strings only on each side.
What about: 
my $str = 'some_str';

my @matches = ($str =~ /^([AGCT]{1,4}),([AGCT]{1,4})$/);

if(2 == scalar @matches){
  for my $match (@matches){
    my %letters = ();
    map { $letters{$_} } ($match =~ /(.)/g);
    exit 0 if(scalar keys %letters != length $match);
  }
}else{
  exit 0;
}

print $str;

[download]
:) also didn't test, maybe doesn't work.

In reply to Re: Regular expression for a comma separated string by igoryonya
in thread Regular expression for a comma separated string by naderra

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