RPA-like single-stranded DNA-binding protein complexes including CST serve as specialized processivity factors for polymerases

Telomere maintenance and replication are highly coordinated processes regulated by a suite of proteins to ensure proper telomere length homeostasis, which, if dysfunctional can lead to cancers and premature aging phenotypes. The critical job of managing single-stranded DNA (ssDNA) during telomere replication is largely performed by conserved heterotrimeric protein complexes. The nucleic acid sequence, length, and structure of telomeres across organisms varies, and as a result the protein players are exquisitely tuned to recognize and manage ssDNA. Recent breakthroughs have shown that these ssDNA-management proteins are extremely structurally similar across humans, yeast, and ciliates. Moreover, these heterotrimeric protein complexes appear to act as processivity factors by a common mechanism made possible by their shared architecture. Here we explore the structural similarities and differences that define these heterotrimeric protein complexes as a specific class of proteins. Furthermore, we propose that these proteins have evolved as specialized activators and processivity factors for the enzymes responsible for replicating telomeres and the rest of the genome.

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