my %hash    = (
 'mus09r' => [ '0,-464,AAACCATCTTGAAAC',
               '0,-350,GGTTCAGGATGGTTT',
               '0,-75,AAAACATCGTGACAC' ],
);

while (my ($file,$val) = each %hash) {
      print ">dataset\n";
      print "$file\n";
      print ">instances\n";
      print join("\n",@{$val}),"\n";
}