Gar1 is an essential small nucleolar ribonucleoprotein (RNP) protein. It contains two GAR domains rich in glycine and arginine residues [2]. Gar1 is localized in the yeast nucleolus and is crucial for cell growth, being involved in pre-rRNA processing as depletion of it impairs the processing of the 35S primary transcript of pre-rRNA and prevents 18S rRNA synthesis [2]. It is also part of the box H/ACA ribonucleoprotein (RNP) complex, which is involved in post-transcriptional RNA pseudouridylation [4].

In the context of the H/ACA RNP complex, Gar1 has several functions. It has a novel SUMO-interacting motif that mediates the interaction between dyskerin and GAR1, and dyskerin mislocalization due to disruption of this interaction can lead to reduced interaction with telomerase RNA [1]. Gar1 reduces the catalytic barrier in H/ACA RNA-guided pseudouridylation by affecting the activation entropy, helps place the target uridine correctly for the pseudouridylation reaction, and is involved in product release [3]. In archaea, Gar1 increases the catalytic activity of Cbf5 in pseudouridylating tRNA, enhances Cbf5's affinity for tRNA, and is crucial for in vivo and in vitro RNA guide-independent formation of Ψ2607 by Cbf5 [5,6].

In conclusion, Gar1 is vital for ribosome biogenesis through its role in pre-rRNA processing and for post-transcriptional RNA modification, specifically pseudouridylation. Its functions within the H/ACA RNP complex, especially in relation to dyskerin and Cbf5, highlight its importance in these biological processes. Although no KO/CKO mouse model-specific findings were in the provided references, understanding Gar1's functions provides a basis for further in vivo studies, which could potentially uncover its role in disease-related pathways.