my $s = 'AYGTACTAGACTACAGACTACAGACATCTACAGACTCATCAGCAGCATATTTA';
my $t = 'ACGTACTAGACTACAGACTACAGACATCTACAGACTCATCAGCAGCATATTKA';

tr/ACGTA-Z/\0\0\0\0_/ for my ($s_, $t_) = ($s, $t);

my $merged = ($s | $t_) & ($t | $s_);
say $merged;