It is difficult to know quite what data structure and form you want from the description (See I know what I mean. Why don't you?). I've assumed you want an array formed with the even lines appended to the odd lines with a space between. Here's an SSCCE to demonstrate one technique for this.
use strict;
use warnings;
use Test::More tests => 1;
my @seq;
my @want = (
'>NM_001 Homo sapiens ADA2 (CECR1) GATCCAA',
'>NM_002 Homo sapiens IKBKG GGAGGTCTTTAGCTTTAGGGAAACCC',
);
while (<DATA>) {
chomp;
if (/^>/) {
push @seq, "$_ ";
} else {
$seq[-1] .= $_;
}
}
is_deeply \@seq, \@want;
__DATA__
>NM_001 Homo sapiens ADA2 (CECR1)
GATCCAA
>NM_002 Homo sapiens IKBKG
GGAGGTCTTTAGCTTTAGGGAAACCC
See also How to ask better questions using Test::More and sample data. HTH.