Your question isn't clear but it seems like what you want is something like:

while(<>) {
    /(\d+) (\d+) (\d+) (\d+).*/ and
        $dna= ($1>0?"a":"") .
              ($2>0?"t":"") .
              ($3>0?"g":"") .
              ($4>0?"c":"");
}
[download]

You can of course replace the >0 with another decision, such as >($1+$2+$3+$4)/10.