for (split ' ', $sequences) {
    if (/\Q$quart1/ and /\Q$quart2/) {
        print "Found both in $_\n";
    }
}

##</code><code>##

while (my ($word) = $sequences =~ /(\S+)/g) {
    if (index($word, $quart1) >= 0 and index($word, $quart2) >= 0) {
        print "Found both in $word\n";
    }
}