The Protein Reviews series serves as a publication vehicle for reviews that focus on crucial contemporary and vital aspects of protein structure, function, evolution and genetics. Volumes are published online first, prior to publication in a printed book. Chapters are selected according to their importance to the understanding of biological systems, relevance to the unravelling of issues associated with health and disease, or impact on scientific or technological advances and developments. Volume 23 presents four review chapters authored by experts in related fields.  The first chapter covers the structure and function of SNM1 family nucleases. Chapter two examines the molecular details of DNA integration by CRISPR-associated (Cas) proteins during adaptation in bacteria and archaea. The third chapter reviews the ordered motions in the nitric-oxide dioxygenase (NOD) mechanism of flavohemoglobin and assorted globins with tightly coupled reductases. Chapterfour reviews structural analyses of the multicopper site of CopG support a role as a redox enzyme. This volume is intended for research scientists, clinicians, physicians and graduate students in the fields of biochemistry, cell biology, molecular biology, immunology and genetics.