The multifunctional SNM1 gene family: not just nucleases.

The archetypical member of the SNM1 gene family was discovered 30 years ago in the budding yeast Saccharomyces cerevisiae. This small but ubiquitous gene family is characterized by metallo-beta-lactamase and beta-CASP domains, which together have been demonstrated to comprise a nuclease activity. Three mammalian members of this family, SNM1A, SNM1B/Apollo and Artemis, have been demonstrated to play surprisingly divergent roles in cellular metabolism. These pathways include variable (diversity) joining recombination, nonhomologous end-joining of double-strand breaks, DNA damage and mitotic cell cycle checkpoints, telomere maintenance and protein ubiquitination. Not all of these functions are consistent with a model in which these proteins act only as nucleases, and indicate that the SNM1 gene family encodes multifunctional products that can act in diverse biochemical pathways. In this article we discuss the various functions of SNM1A, SNM1B/Apollo and Artemis.