As metioned already, no need for the character class.. Also, (although i tend to prefer the 2 separate statements as well), this can be written as one: 
$dna =~ s/(^N+|N+$)//g;

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In reply to Re^2: Removing Flanking "N"s in a DNA String by davidrw
in thread Removing Flanking "N"s in a DNA String by monkfan

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