my %acronyms;

my $text= "An important class of transcription factors called general transcription factors (GTF) are necessary for transcription to occur. The Most common GTF's are TFIIA, TFIIB, and TFIIE.And a few more not mentioned here.";

my @words = split('\W+', $text);

foreach(@words) {
   	if($_ =~ m/^[A-Z]+$/){ $acronyms{$_}++; }
}
foreach( keys(%acronyms) ){ print "$_ seen $acronyms{$_} times\n"; }