You dont need to use regular expressions to solve your problem. An order of magnitude less CPU intensive to use index and substr. Make sure your XML tags are ALWAYS the same before choosing to use index. '<GENE>' and '<Gene>' and '< GENE>' are totally different to index.

$string = 'Furthermore , expression of <GENE> Vpu </GENE> in Jurkat T 
+cells rendered them more susceptible to <GENE> Fas </GENE> - induced 
+death ';
$start = 0;
while (($beg = index($string, '<GENE>', $start)) > -1)
{
     
     $end = index($string, '</GENE>', $start)+7;
     substr($string, $beg, ($end-$beg), '');
     $start = $end;
}
print $string;
[download]

I do notice a double space left where the GENE tag used to be though.

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.