Remote homology and functional genetics unmask deeply preserved Scm3/HJURP orthologs in metazoans
Hollis, J. A.; Stonick, J. A.; Topalidou, I.; Young, J. M.; Moens, C. B.; Lehrbach, N. J.; Campbell, M. G.; Malik, H. S.
Show abstract
In most animals and fungi, centromere identity and function depend on the Scm3/HJURP chaperone, which deposits CENPA at centromeres. However, Scm3/HJURP orthologs appeared to be missing in insects, nematodes, many vertebrates, and other metazoans, suggesting radical chaperone replacement in these lineages. Here, we combine remote homology detection, AlphaFold-based structural modeling, and functional genetics in zebrafish and Caenorhabditis elegans to identify previously unknown Scm3/HJURP orthologs that localize to centromeres and whose loss causes catastrophic mitotic failure. We further show that Drosophila CAL1, long considered a functional analog, is instead a highly diverged Scm3/HJURP ortholog. Despite rapid primary-sequence divergence, predicted and known structures reveal a broadly conserved CENPA-H4-binding scm3 fold across fungi, vertebrates, nematodes, insects, and basally-branching metazoans. Our work demonstrates how rapid divergence can obscure the broad conservation of essential centromere machinery and provides a broadly applicable strategy to unmasking missing orthologs. Summary statementAnimals encode a rapidly evolving, essential cell cycle gene previously thought to be absent.
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