tr/0123/TCAG/

##</code><code>##

my $dna = '';
use constant CHUNKSIZE => 2048;
for (my $offset = 0; $offset < length($raw); $offset += CHUNKSIZE) {
   $dna.= join '', @CONV[ unpack 'C*', substr $raw, $offset, CHUNKSIZE ];
}

##</code><code>##

s/(.)/$CONV[ord $1]/sge