Csm4

Csm4 is a protein name used for two distinct families of proteins in biology, reflecting its occurrence in different domains. In budding yeast, Csm4 denotes a meiosis-specific protein associated with the nuclear envelope that participates in telomere-led chromosome movements during meiotic prophase. It functions together with Mps3 and Ndj1 to anchor chromosome ends to the nuclear envelope, promoting telomere clustering and homologous chromosome pairing, which supports recombination and the progression of the synaptonemal complex. Mutants lacking Csm4 exhibit defects in bouquet formation and reduced recombination, and Csm4 expression is restricted to meiotic cells.

In bacteria and archaea, Csm4 is a subunit of the type III CRISPR-Cas interference complexes (often referred to as the Csm complex). It is a non-enzymatic component that participates in assembling and stabilizing the multi-subunit effector complex, which uses CRISPR-derived RNA to recognize nucleic acid targets. The exact role of Csm4 can vary among organisms, but it is generally viewed as part of the structural backbone of the Csm complex alongside other subunits such as Csm1 (Cas10), Csm2, Csm3, Csm5, and Csm6. In many systems, the Csm complex interferes with RNA targets and, in some contexts, DNA targets as well, with Csm4 contributing to proper complex assembly rather than catalytic activity.

Because the same abbreviation Csm4 is used for proteins in phylogenetically distant contexts, interpretation should rely on the biological context to distinguish yeast meiotic Csm4 from CRISPR-associated Csm4.