#!/usr/bin/perl -w
use strict;

my $a1="CCCATCTGTCCTTATTTGCTG";
my $a2="ACCCATCTGTCCTTGGCCAT";
my $a3="CCACCAGCACCTGTC";
my $a4="CCCAACACCTGCTGCCT";

$a1=~s/(ATCTG|ATTTG)/\[$1\]/g;
$a2=~s/(CCATC)/\[$1\]/g;
$a3=~s/(CCACC|CCAGC|GCACC)/\[$1\]/g;
$a4=~s/(CCAAC|ACACC)/\[$1\]/g;

print "$a1\n$a2\n$a3\n$a4\n";