Using first might not be a great idea. If $curEntry is the empty string "", and @taxR does actually contain an empty string (so you should expect a match), then first will end up returning false.

The any function from List::MoreUtils is probably a better choice.

As to your question, you might get better performance from a hash:

my @taxR = ("PLRV1", "PMTVS", "PVXHB");

# Copy the array into a hash.
# Make sure you only do this once.
my %taxR = map {$_ => 1} @taxR;

my $curEntry = "PMTVS";
if (exists $taxR{$curEntry}) {
    print "do rest of stuff";
}
[download]