Complex sentence: Meganucleases are endodeoxyribonucleases that are characterized by a large recognition site (double-stranded DNA sequences of 12 to 40 base pairs); as a result of its size, this site generally occurs only once in any given genome.
Split into simpler sentences: Meganucleases are endodeoxyribonucleases that are characterized by a large recognition site (a double-stranded DNA sequence of 12 to 40 base pairs). As a result of its size, this site generally occurs only once in any given genome.