my $seq = "G_I1E2_GTGGAG^303CTGgacgCCCTGC_I2E3_TACA";
$seq =~ s/[^ACTGactg]//g;
my @result = $seq =~ /[ACTG]+/g;
say for @result;

##</code><code>##

perl -wE 'say for "G_I1E2_GTGGAG^303CTGgacgCCCTGC_I2E3_TACA" =~ s/[^ACTGactg]//gr =~ /[ACTG]+/g;'