U4atac

U4atac is a small nuclear RNA that forms part of the minor (U12-type) spliceosome. In humans, it is encoded by the RNU4ATAC gene. U4atac functions together with U6atac to compose the U4atac/U6atac di-snRNP, which participates in the splicing of U12-type introns, a minority class of introns found in a subset of essential genes.

Within the spliceosome cycle, U4atac base-pairs with U6atac and other snRNPs to recognize the 5' splice sites and branch points of U12-type introns. Upon activation, U4atac is displaced, allowing U6atac to engage in the catalytic steps of splicing. Although U12-type introns are relatively rare, their correct processing is crucial for proper gene expression, particularly during development and in tissues with high demands for accurate splicing.

Genetics and disease: Pathogenic variants in RNU4ATAC have been linked to developmental disorders, most notably Joubert syndrome and related ciliopathies; other reports associate RNU4ATAC mutations with microcephaly with chorioretinopathy and broader neurodevelopmental syndromes. The mutations may affect snRNA processing, stability, or base pairing, leading to impaired splicing of U12-type introns.

Evolution and conservation: U4atac is conserved across eukaryotes that retain the minor spliceosome components. As with other small nuclear RNAs, U4atac is a component of small nuclear ribonucleoprotein particles, contributing to the fundamental process of pre-mRNA splicing.